JPS6071027A - Controlling method of ammonia injection amount in dry waste gas denitration apparatus - Google Patents

Abstract

PURPOSE:To prevent the amount of unreacted NH3 gas from exceeding a predetermined value even if the temp. of a catalyst layer is changed, by detecting the temp. of the catalyst layer while comparing the operation result of the detected temp. with the set signal of the amount of NH3 to be injected to control the actual amount of NH3. CONSTITUTION:The temp. of a catalyst layer 2 is detected by a detector 15 and the signal 15a thereof is inputted to a function generator 16. Herein, function for outputting an NH3/NOx ratio when the leak amount of unreacted NH3 is set so as not to exceed a predetermined value is assembled with due regard to a denitration rate to the temp. of the catalyst layer. The signal 16a of the function generator 16 and the signal of the NH3/NOx ratio set by a setting device 6 are inputted to a low value preference circuit 17 and the lower signal 17a thereof and a NOx total amount signal 5a are multiplied by a multiplier 7. On the basis of the injection NH3 amount setting signal 7a therefrom and the signal 8a from an NH3 gas amount detector 8, a signal 9a for regulating the opening degree of an NH3 injection amount control valve is outputted from an NH3 gas amount controller 9 to control an NH3 injection amount.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for controlling the amount of ammonia nitrate injected into combustion exhaust gas from a boiler or the like.

Technical background of the invention and its problems] FIG. 1 shows a denitrification device that reduces nitrogen oxides (hereinafter referred to as NOx) in combustion exhaust gas with ammonia (hereinafter referred to as NH3). In the figure, NOx in exhaust gas 2 from a combustor such as a boiler (not shown) is NH
3 NH introduced from injection nozzle 1, gas n and catalyst layer 2
is subjected to a reduction reaction and released to the outside of the system as processing gas d.

In this denitration equipment, it is necessary to control the amount of NH and gas n to be injected in proportion to the amount of NOx in the exhaust gas V.
This conventional control method was performed in the following steps.

That is, in FIG. 1, the exhaust gas flow rate signal 3a from the exhaust gas flow rate detector and the NOx concentration signal 4a from the NOx concentration detector 4 are multiplied by a multiplier 5, and NO in the exhaust gas V is calculated.
To determine the total amount x, multiply this NOx total amount signal 5a and the NH3/NOx ratio setting signal 6a set by the setting device 6 by a calculation of 7, and then calculate the NH to be injected and the gas flow rate setting signal 7a.
I put it on. This NH, gas flow rate setting signal 7a and NH, NH from gas flow rate detector 8, and NH from gas flow rate signal 8a.
, calculated by the gas flow rate controller 9, NH! The NH gas current control valve 10 controls the flow of the NH3 gas n injected from the NH injection nozzle 1 using the output signal 9a of the gas flow rate controller 9.
Adjust the opening.

Here, the settings set by the setting device 6 are NH, /NO.
The operator inputs the NOx concentration signal 11a from the NOx concentration detector 11 in the process gas d to the NOx concentration recorder 12, checks the NoXa degree in the process gas d, and then ．． /NOx ratio is set. At this time, NH
If the ratio of 3/NOx is too high, a phenomenon occurs in which NH and gas n leak unreacted into the processing gas d.
Not only will this have a negative impact on the equipment after the exit of the denitration equipment, but it may also become a cause of secondary pollution. For this reason, the NH8 concentration in the processing gas d is also monitored.

However, combustors such as boilers, which are the source of NOx, usually undergo load fluctuations, and the temperature of the flue gas fluctuates accordingly.Especially when starting the boiler, the temperature of the flue gas is low; As the load increases, the combustion exhaust gas temperature also increases. On the other hand, as the temperature of the combustion exhaust gas decreases, the temperature of the catalyst layer 2 also decreases, the amount of NH adsorbed onto the surface of the catalyst layer increases, and the denitrification efficiency decreases. Additionally, as the temperature rises, NH3 adsorbed at low temperatures is desorbed and released into the exhaust gas, and the NH,/NOx ratio increases, leaving unreacted NH,
There was a problem with the release of Therefore, the amount of operation is
In order to avoid the adverse effects caused by unreacted NHs, there was a problem in that the ratio of NH8/NOx had to be changed using the setting device 6 every time the load changed.

Further, the NH31 degree detector 13 is currently commercially available using chemiluminescence method, etc., but it is currently unreliable and the NH31 degree detector 13 detects NH from the NH3 concentration detector 13.

Incorporating the concentration signal 13a into the control system is undesirable because it may conversely disturb the control system.

OBJECT OF THE INVENTION The object of the present invention is to provide a method for controlling the amount of ammonia injection in a dry flue gas denitrification device that prevents unreacted NH3 gas from exceeding a predetermined value even when the temperature of the catalyst layer changes depending on the temperature of the combustion exhaust gas. It is on offer.

[Summary of the invention]

The method for controlling the amount of ammonia injection in a dry flue gas denitrification device according to the present invention detects the temperature of the catalyst layer, inputs this temperature signal to a function generator, and sets the output signal of this function generator and the amount of NH to be injected. This system is characterized in that the signals are compared using a low value priority circuit, and the actual amount of NH8 to be injected is controlled using the output signal.

Embodiments of the Invention] The present invention will be described below with reference to an embodiment shown in FIG. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts, so the explanation thereof will be omitted.

A control device for carrying out the ammonia injection amount control method according to the present invention is shown in FIG. In FIG. 2, the temperature of the catalyst layer 2 is detected by a temperature detector 15, and the temperature signal 15
a is input to the function generator 16.

This function generator 161 considers the denitrification rate with respect to the temperature of the catalyst layer, which is an input signal, and outputs unreacted NH into the process gas.
NH3 when the leakage amount of
A function is incorporated to output the ratio of /NOx.

The output signal 16a of the function generator 16 and the setting signal 16a of the NH3/NOx ratio set by the setting device 6 are input to the low value priority circuit 17, and the lower of the two is set as the output signal 17a. 17a and NOx total amount signal-q5a
are multiplied by the multiplier 7, and the NH and gas flow rate setting signal 7a to be injected is calculated. NH3 gas flow rate setting signal 7a from and NH3 gas flow rate signal 8a from NH, gas flow rate detector 8
The NHs gas flow rate controller 9 calculates the amount of NHs gas n to be injected from the NH3 injection nozzle 1 using the output signal 9a of the NH3 gas flow rate controller 9. Adjust.

FIG. 3 shows the function generator 1 when NHs gas is injected so that the amount of unreacted NH gas leaking into the process gas does not exceed a predetermined value at the temperature of the catalyst layer 2 and the temperature at that time.
6 represents the ratio of NH,/NOx treated in step 6.

In the ammonia injection amount control device shown in FIG. 2, if the operator first sets the NH3/NOx ratio to the normal setting value a, if the temperature of the catalyst layer 2 is low, unreacted NH,
While the limit set value is already limited so that the amount of gas does not exceed a predetermined value, NH and gas are injected, and the temperature of the catalyst layer 2 increases until it reaches a point C where it intersects with the normal set value a. After reaching this point C, the injection amount of NH and gas is controlled by the normal set value a. In Figure 3, the part where the temperature of the catalyst layer is low is cut out because if the temperature of the catalyst layer 2 is particularly low, the denitrification rate will decrease even if NH, is injected. Even if gas is injected, there is almost no denitrification function.

This control set value is incorporated into the function generator 16, and a comparison with the normal set value a from the setter 6 is performed by a low value priority circuit 17. In this example, the temperature of the catalyst layer 2 was considered at only one point, but it is also possible to detect it at multiple points and calculate the average temperature for use. It is also possible to detect and use the temperature at the inlet or outlet.

〔Effect of the invention〕

As described above, in the present invention, the temperature of the catalyst layer is detected, this temperature signal is input to the function generator, and the output signal of this function generator is compared with the ammonia injection amount setting signal using the low value priority circuit. By controlling the actual amount of ammonia injected using the output signal, the denitrification device can be continuously and automatically operated so that the amount of ammonia leaking into the process gas does not exceed a predetermined value. Moreover, it is now possible to automatically operate NHj injection control from the time of startup, so even during normal operation, even if the NH injection amount is accidentally set to a high value,
This has advantages such as eliminating the problem of excessive leakage ammonia.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an ammonia injection amount control device in a conventional dry type flue gas denitrification device, and Fig. 2 is an ammonia injection amount control device to which the ammonia injection amount control method in a dry type flue gas denitrification device according to the present invention is applied. FIG. 3 is a system diagram showing an example of the NH3/NO ratio at the temperature of the catalyst layer of the present invention.
FIG. 3 is a characteristic diagram showing the restriction relationship of the ratio of x. 1... NH3 injection nozzle 2... Catalyst layer 3... Exhaust gas flow rate detector 4, 11... NOx concentration detector 5.
7... Multiplier 6... Setting device 8... NH, Gas flow rate detector 9... NH, Gas flow rate controller 10... NH, Gas flow rate control valve 12...
NOx concentration recorder 13...NH, concentration detector 14.
...NH, concentration recorder 15...Catalyst layer temperature detector 1
6...Function generator 17...Low value priority circuit (8733) Representative patent attorney Yoshiaki Inomata (and 1 other person) Figure 1 Figure 2 Cause

Claims (1)

[Scope of Claims] (1) In a dry flue gas denitrification device that injects ammonia as a reducing agent into the combustion exhaust gas of a boiler or the like containing nitrogen oxides and decomposes and removes the nitrogen oxides, a catalyst in the device A low value priority circuit compares the ratio between the amount of ammonia gas and the amount of nitrogen oxides corresponding to the temperature in the layer and the preset ratio between the amount of ammonia gas and the amount of nitrogen oxides, and the output signal is used to select the ammonia note (2). ) From this, when measuring the temperature of the catalyst layer,
This method monitors the denitrification rate corresponding to the temperature and automatically controls the injection of ammonia when the temperature of the catalyst layer is low, so that the amount of leaked ammonia does not exceed a predetermined value. (3) By measuring the temperature of the catalyst layer, the denitrification efficiency at that time is monitored, and even if the setting signal that sets the ratio of nitrogen oxides to ammonia as the setting value is incorrectly set to a high value, the amount of leaked ammonia is maintained at the specified level. A method for controlling the amount of ammonia injection in a dry flue gas denitrification device according to claim 1, characterized in that the amount of ammonia injected into a dry flue gas denitrification device is controlled so as not to exceed a value. (4) In a dry flue gas denitrification device that injects ammonia, a reducing agent, into the combustion exhaust gas of a boiler or the like containing nitrogen oxides and decomposes and removes the nitrogen oxides, the temperature of the catalyst layer in the device is detected. , input this temperature signal to the function generator,
Claim 1, characterized in that the output signal of the function generator and the ammonia injection amount setting signal are compared in a low value priority circuit, and the output signal is used as the setting signal for actual ammonia injection amount control. A method for controlling the amount of ammonia injection in the dry flue gas denitration equipment described above. (5) The dry smoke exhaust gas according to claim 4, wherein the function generator outputs a ratio of nitrogen oxides and ammonia in consideration of the denitrification rate at the temperature of the catalyst layer of the input signal. Ammonia injection amount control method in denitrification equipment.