JPS6211529A - Controlling method for amount of ammonia to be injected for denitration apparatus - Google Patents

Abstract

PURPOSE:To prevent the decrease of degree of denitration by allowing a signal in a period of burner ignition or/and in a period of the changeover of a damper of a wind box to precede, actuating a signal injecting NH3 in the specified amount or more and performing a denitration reaction. CONSTITUTION:An output signal is obtained from a multiplier 24 on the basis of both an NOx concn. signal 21 of a reactor inlet and a load signal 22 of a boiler. Also the relays 35, 36 are opened with the signals 33, 34 in a period of burner ignition or in a period of the changeover of a damper of a wind box and a signal sent from a signal generator 37 is added to an output signal sent from an adder 24 in an adder 40 via an adder 38 and a first-order lag setter 39 to use it as a set signal 25. Thereby NH3 is injected the specified amount or more in a period of burner ignition or in a period of the changeover of the damper of the wind box to prevent the decrease of degree of denitration.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling the amount of ammonia injected into a denitrification device for a giller.

(Conventional technology) In conventional denitrification equipment, NH injection amount control is based on the NOx concentration at the denitrification equipment inlet (hereinafter referred to as inlet NOx).
，The amount is supposed to be injected.

On the other hand, with current denitrification catalysts, the denitrification reaction is slow and the control instruments including the analyzer are delayed, so if a fluctuation (sudden change) in inlet NOx occurs that is larger than the normal load increase rate, a satisfactory response cannot be achieved. Therefore, the required denitrification performance cannot be secured.

That is, in the denitration apparatus, as shown in FIG. 1, the atmosphere is compressed by a forced draft fan 1, heated by a steam-type air preheater 2, and further heated by an air preheater 3. Injected into Pillar 4. on the other hand? The exhaust gas generated in the filter is denitrified in the denitrification reactor 5, heated (heat recovered) in the air preheater 3, and electrostatically precipitated 1!
! The dust is removed in step 6 and is led to the chimney 7 and released into the atmosphere.

On the other hand, N'H3 is stored as a liquid in a tank 8, vaporized in a vaporizer 9 according to the consumption amount, and injected into the flue gas from an NH3 injection nozzle 14 located upstream of the denitrification reactor 5 as a reducing agent for the denitrification reaction described below. be done.

p NOx (No or NO□) due to injected NH3
reacts as shown below to form harmless nitrogen (N2) and water vapor (H
2O).

In addition, it improves the spray effect when injecting NH3 into the flue, and
In order to dilute NH6 to below the explosion limit, the NH6 is preliminarily diluted with air in a mixer 13 before being introduced into the air duct upstream of the air preheater 3 and injected into the flue gas.

or? The amount of exhaust gas is determined as a function of the load signal 15, and this value is multiplied by the value detected by the NOx monitor 20 of the reactor's NOx 9 degrees to determine the total amount of NOx that enters the reactor. NH31- is injected according to the amount of NH3 injection, but the actual value measured at the orifice 11 is fed back as the amount of NH3 injection actually injected to improve control accuracy.

In the drawing, 10 is an accumulator, 12 is an ammonia flow control valve, 13 is a mixer, 17 is an AT calculator, and 18
is a regulator, and 19 is a flow rate transmitter.

To explain the conventional control function for the amount of ammonia, as shown in FIG. The signal is applied to the multiplier 24 by the combined setting signal 25 (used as the total NOx value, required NH3
control valve 29 via regulator 26. Due to problems with the control device, the output signal (analog) of the regulator 26 is converted into a pulse signal by the pulse generator 27, and further converted into an air signal by the electro-pneumatic converter 28.

On the other hand, in order to improve the accuracy of the control amount, the ammonia injection amount signal 30 flowing at that time is set as the flow rate value of the flattener 3 and the regulator 26
It is returned as a feedback signal (measurement signal 32゛).

This is so-called feedback control.

Therefore, the development of the cyanmonia injection amount control valve 29 is controlled by changing the setting signal 25 according to changes in the reactor inlet NOx concentration signal 21 and the boiler load signal 22.
Due to the delay in the denitrification reaction, it was not possible to secure the required denitrification rate shown below in response to sudden changes in the NOx concentration at the reactor inlet when one burner was ignited or when the wind box was switched.

Although the denitrification reaction exhibits a chemical reaction as shown in equation (1) above, it usually takes 30 minutes or more to stabilize (a) with response characteristics as shown in FIG. 4 (2).

Incidentally, FIG. 5 shows an example of the NT (step change in three quantities) characteristic.

(Problems to be Solved by the Invention) In view of the current situation, the present invention conducted extensive research and was able to significantly improve the denitrification performance by finding out that timing affects the denitrification performance.

(Means for Solving the Problems) The present invention is characterized in that ammonia in the denitration equipment is carried out by preceding the signal for switching the ammonia injection pump and by preceding the signal for injecting more than a specified amount of ammonia. It is something to do.

(Embodiment) The method of the present invention is an improvement on the setting signal 25 in the conventional control method (FIG. 3).As shown in FIG. ．．
34 years old? Open the U switch 5.36 and open the signal generator 37
The signal from the adder 4Q is added to the output signal of the setting signal multiplier 24 via the adder 38 and the -order delay setter 39, and is used as the setting signal 25. That is, when one burner is ignited or when the wind box damper is switched, a signal is input in advance to the injection control to input more than the specified amount of NH in each signal.

Note that the output signal of the next delay setter 38 is 2 to 2 as shown in the output 41.
The signal level increases in 5 minutes.

In this way, changes in the denitrification rate were measured for the control method according to the present invention (when a preceding signal is provided) and the conventional control method (when there is no preceding signal). The results are as follows:
As shown in the figure.

As is clear from Fig. 6, in the method of the present invention, the decrease in the denitrification rate due to excessive injection of NH due to the burner ignition (or wind box switchover) signal was only about 70%, which was significantly alleviated. In the conventional method, the denitrification rate sharply decreased (below 60 degrees) as the NOx at the reactor inlet increased due to single ignition (or switching of the windbox damper).

(Effects) As detailed above, the method of the present invention is industrially useful because the denitrification rate is extremely reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of a conventional denitrification device, Fig. 2 is a schematic explanatory diagram showing a method for controlling the amount of ammonia injection in the denitrification device of the present invention, and Fig. 3 is a schematic explanatory diagram showing a method for controlling the amount of ammonia injection in the conventional denitrification device. 4 is an explanatory diagram of the response characteristics in the denitrification reaction, FIG. 5 is an explanatory diagram of the step change characteristics of the amount of ammonia, and FIG. 6 is a diagram of the relationship curve between time and denitrification rate. DESCRIPTION OF SYMBOLS 1... Forced draft fan, 2... Air preheater, 3... Air preheater, 4... Ira, 5... Denitrification reactor, 6...
... Electrostatic dust collector, 7 ... Chimney, 8 ... Liquid ammonia tank, 11 ... Orifice, 14 ... Ammonia injection nozzle, 21 ... Reactor inlet NOx concentration detection signal, 22 ... -Ira load signal, 23...function generator, 24...multiplier, 25...setting signal, 3o...
- Ammonia injection amount detection signal, 33... Burner ignition signal, 34... Wind box Dan/4' switching signal, 37... Signal generator, 38... Adder, 39... - next delay Setter, 40... adder.

Claims (1)

[Claims] In the method of injecting ammonia in a denitration equipment,
A method for controlling the amount of ammonia injected into a denitrification device, characterized in that a denitrification reaction is carried out by activating a signal for injecting more than a specified amount of ammonia by preceding a signal when igniting a burner and/or switching a wind box damper.