JPS60216829A - Denitration apparatus - Google Patents

Abstract

PURPOSE:To maintain denitration efficiency at a fixed level in a denitration apparatus by determining the content of NOx and the amt. of NH3 corresponding thereto, controlling the amt. of NH3 to be injected from the difference between the value of injected NH3 and required NH3, thus correcting the amt. of NOx by outputting correcting output for a specified time. CONSTITUTION:The concn. of NOx at the inlet of a denitration reactor is found by an originator 41, and the flow rate thereat is found by an originator 42, and the total amt. of NOx is found by a multiplier 43. Further, the amt. of NH3 is found by an originator 44, and the required amt. of NH3 is found from said sensed value and the total amt. of NOx using a molar ratio operator 45, and a multiplier 46 succeedingly. The difference between the required amt. and injected amt. of NH3 is inputted to the controller 48, thus, an NH3 injecting valve 8 is controlled to control the amt. of NH3 to be injected. When the operation condition of a boiler varies, a relay circuit 50 is closed for a specified time corresponding to the variation. A correction signal is given to an adder 51 to add a correction signal to the total amt. of NOx, which is inputted to the controller through a subtractor 47 to control the amt. of NH3 to be injected. Thus, the concn. of NOx at the outlet of the denitration apparatus is held at a fixed level.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a denitrification device used for treating exhaust gas from, for example, a coal-fired boiler.

Nitrogen oxides (NO) contained in the combustion gas of coal-fired boilers
The denitrification device, which is a device for reducing x), has a configuration as shown in FIG. That is, in the figure, 1 is a boiler furnace, and 2 is a push-in passage x for blowing air into the boiler furnace 1.
It is i. 3 is 1l1 which reduces nitrogen oxides contained in the flue gas from the boiler furnace 1 by reaction with ammonia.
21i1 is a reactor, and 4 is an induced passage J! which leads out the gas from the denitrification reactor 3. 1111.5 is a chimney for discharging this extracted gas to the outside. Exhaust smoke from the boiler furnace 1 is guided by a duct 6 to a chimney 5 via a denitrification reactor 3 and an induced draft fan 4, and is discharged from the chimney 5.

7 is an ammonia gas generation facility for generating ammonia gas, and 8 is an injection control valve for the ammonia gas generated by the ammonia gas generation facility 7. Reference numeral 9 denotes an ammonia gas injection control device for adjusting the amount of ammonia gas, and the ammonia gas injection control device 9 adjusts the opening degree of the ammonia gas injection valve 8, so that the ammonia gas generated from the ammonia gas generation equipment 7 is controlled by the ammonia gas injection control device 9. This controls the amount of water injected into the denitrification reactor 3.

That is, in such a configuration, air is blown to the boiler furnace 1 by the forced draft t12, and the boiler furnace 1 is caused to burn. Exhaust smoke from boiler furnace 1 is passed through
At this time, the nitrogen oxides contained in the flue gas are reduced by the denitrification reactor 3 by reaction with ammonia.

Ammonia gas generated from the ammonia gas generation equipment 7 is injected into the denitrification reactor 3.
is reduced by reacting the injected ammonia gas with nitrogen oxides.

In order to perform an efficient denitrification reaction, the ammonia gas injection control device 9 adjusts the opening degree of the ammonia gas injection valve 8 according to the nitrogen oxide concentration in the flue gas, and the ammonia gas generated from the ammonia gas generation equipment 7 is Control the amount of gas injected into the denitrification system [3. This makes it possible to suppress the amount of gas to a nitrogen oxide concentration within the specified concentration while exhausting smoke.

By the way, target value control of the amount of ammonia gas (NH3) for denitrification reaction in the denitrification apparatus in such a system is performed by a system as shown in FIG. In other words, NOx detects the NOx concentration at three points in the denitrification reactor (point A in Figure 1) and generates a detection signal according to the detected concentration.
A concentration transmitter 21 and a supply air amount transmitter 22 that detects the amount of air blown to the boiler furnace 1 and generates a detection signal according to the detected amount of air blown are provided, and this rain detection signal is given to a multiplier 23 for multiplication. , calculate the total amount of NOx at point A at the inlet of the denitrification reactor.

On the other hand, an ammonia gas amount transmitter 24 is provided which detects the amount of ammonia gas injected into the denitrification reactor 3 and generates a detection signal according to the detected amount. The amount of NOx and the total amount of NOx calculated above are fed to the molar ratio calculator 25 to calculate their molar ratio.

That is, the molar ratio calculator 25 calculates the amount of ammonia gas and NO.
The molar ratio is calculated from the ratio of x to the total amount, and the thus determined molar ratio is input to the multiplier 26 together with the determined total amount of NOx, and the two are multiplied to determine the required amount of NH3. This required amount of NH3 and the ammonia gas port output from the ammonia gas amount transmitter 24 are given to a subtractor 27 to calculate the difference between the amount of ammonia gas and the required amount of NH3, and the difference is given to the controller 28 as a deviation signal. The controller 28 outputs a valve opening control signal such that the deviation signal becomes zero, and this valve opening division signal is used to control the opening of the ammonia gas injection valve. The opening degree of the ammonia gas injection valve 8 is adjusted, and the amount of ammonia gas generated from the ammonia gas generation equipment 7 to be injected into the denitrification reactor 3 is controlled.

The control characteristics of this control system are shown in FIG.

That is, as shown in (a), when the total amount of NOx at the inlet of the denitrification reactor suddenly changes, the amount of ammonia gas injected increases accordingly, but this increase is made by the output of each transmitter 21, 22, and 24. Therefore, it changes with a slight delay as shown in (b). Therefore, the outlet N0xl of the denitrification reactor 3! The degree of NO
The X concentration rises rapidly, and then the amount of ammonia injected increases, so it gradually returns to the target value, but due to the lag factor, the concentration once drops too much, then rises again and becomes stable.

This type of control system is one example of various control systems, and there are many others, but all conventional control systems respond to sudden changes in the NOx concentration at the inlet of the denitrification reactor, as described above. The delay caused by the denitrification reactor 3 itself could not be compensated for.

This is because the control system cannot predict sudden changes in the NOx concentration at the inlet of the denitrification reactor. Further, in coal-fired boilers, such a phenomenon often occurs at a certain point in the startup/stop process of the coal burner.

For example, in the case of a pressurized mill, it is known that this occurs when the coal feeder is started, and when the hot air to the mill is cut off during the shutdown process. Therefore, it is desired to develop a denitrification device that prevents changes in exhaust NOx concentration due to such sudden changes in NOx concentration.

The present invention has been made in view of the above circumstances, and is a denitrification device that denitrates nitrogen oxides contained in boiler exhaust gas by reacting with injected ammonia gas. A means for obtaining the amount of nitrogen oxide, a means for calculating the required ammonia gas amount from the above-mentioned injected ammonia gas amount and nitrogen oxide amount, and a deviation between the required ammonia gas amount and the above-mentioned injected ammonia gas amount, and a method according to this deviation. means for generating a control output for the amount of ammonia gas to be injected; and means for correcting the amount of nitrogen oxides by providing a correction output for a predetermined period of time in accordance with the denitrification reaction delay characteristic of the denitrification device in response to changes in the operating state of the boiler; A denitrification device that uses a control system that prevents the concentration of discharged nitrogen oxides from changing suddenly even if the nitrogen oxide concentration at the denitrification device inlet suddenly changes when the boiler operating state changes, that is, when the operating state changes. The purpose is to provide

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5.

FIG. 4 is a block diagram showing the configuration of a control system that controls the injection amount of ammonia gas (NH3) for the denitrification reaction in the denitrification apparatus according to the present invention. In the figure, 41 indicates the population of the three denitrification reactors (
A NOx concentration transmitter 42 detects 11 degrees of NOx at point A in FIG. A supply air amount transmitter 43 that generates a detection signal according to II multiplies the detection signals output from the NOx concentration transmitter 41 and the supply air 1 transmitter 42, and calculates the total amount of NOx at point A at the inlet of the denitrification reactor. 44 is an ammonia gas amount transmitter that detects the amount of ammonia gas injected into the denitrification reactor 3 and generates a detection signal according to the detected amount;
Reference numeral 45 denotes a molar ratio calculator, which calculates the molar ratio A based on the ammonia gas amount detected by the ammonia gas amount transmitter 44 and the total amount of NOX calculated above. 46 is a multiplier that multiplies the molar ratio determined by the molar ratio calculator 45 by the total amount of NOx determined above to determine the billed amount.

47 is a subtracter, and the NHi output from the multiplier 46 is
A deviation signal is obtained by subtracting the required amount and the ammonia gas amount output from the ammonia gas amount transmitter 44 to find the difference between the ammonia gas amount and the NH3 required amount. Reference numeral 48 denotes a controller, and this controller 48 outputs a valve opening control signal such that the deviation signal becomes zero, and applies this valve opening control signal to the ammonia gas injection valve 8 to open the valve. By controlling the opening degree of the ammonia gas injection valve 8, the amount of ammonia gas generated from the ammonia gas generation equipment 7 to be injected into the denitrification reactor 3 is controlled. The configuration up to this point is basically the same as that in FIG. 2 above.

The present invention differs in that a correction signal generator 49 is further added, and the output of this correction signal generator 49 is added to the output of the multiplier 43 when the operating state of the boiler changes. That is, on the output side of the correction signal generator 49, there is a relay 5 that operates and closes for a predetermined time when the operating state of the boiler changes.
0 and adds the output of the correction signal generator 49 outputted via this relay 50 to the output of the multiplier 43 and supplies it to the multiplier 46.
It is provided at the front stage of 6.

Next, the operation of this device having the above configuration will be explained.

NOx 11 degree transmitter 41 that detects the NOx concentration in the denitrification reactor 3 population and generates a detection signal according to the detected concentration
The supply air amount transmitter 42 detects the amount of air blown to the boiler furnace 1 and generates a detection signal according to the detected air amount, detects the NOx concentration and the amount of air blown, and sends this rain detection signal to the multiplier 43. Given and multiplied, NOx at the denitrification reactor inlet point A
Calculate the total amount.

On the other hand, the ammonia gas amount is detected by an ammonia gas amount transmitter 44 that detects the amount of ammonia gas injected into the denitrification reactor 3 and generates a detection signal according to the detected amount,
The amount of ammonia gas detected and the NO calculated above
The total amount of x is given to the molar ratio calculator 45 to calculate these molar ratios.The obtained molar ratio is inputted to the multiplier 46 together with the total amount of NOx determined above, and both are multiplied, NH! The required quantity is determined. This NHs request amount and the ammonia gas amount output from the ammonia gas amount transmitter B44 are subtracted and given to 1$47, and NH! Calculate the difference in the amount of ammonia gas against the required amount,
It is given to the controller 48 as a deviation signal. The controller 48 outputs a valve opening degree control signal such that the deviation signal becomes zero, and applies this to the ammonia gas injection valve 8 to control the valve opening degree.

Thereby, the opening degree of the ammonia gas injection valve 8 is adjusted, and the amount of ammonia gas generated from the ammonia gas generation equipment 7 to be injected into the denitrification reactor 3 is controlled.

The above is the control form under normal conditions. Now, if the operating state of the boiler furnace 1 changes, the relay 50 closes for a predetermined period of time in response to this change. As a result, the relay 50
The correction signal output from the correction signal generator 49 is given to the adder 51 via and is applied to the multiplier 46. Therefore, the above predetermined time,
The deviation signal outputted from the subtracter 47 is corrected by a correction signal valve and then provided to a controller 48. Therefore, the controller 48 outputs a valve opening control signal such that the deviation signal becomes zero, and this signal is applied to the ammonia gas injection valve 8 to control the valve opening, so that the ammonia gas generated by the ammonia gas generation equipment 7 is By controlling the amount of ammonia gas injected into the denitrification reactor 3, it becomes possible to adjust the amount of ammonia gas injected in response to sudden changes in the NOx concentration at the denitrification device inlet when the boiler operating conditions change, and the boiler Even if the operating conditions change, the NOX concentration at the outlet of the denitrification device can be kept constant.

FIG. 5 shows the control characteristics of the above control system.

That is, when the operating condition changes, the total amount of NOx at the inlet of the denitrification reactor changes suddenly as shown in (a), but since there is some delay in this change, the above correction signal is added for a predetermined period of time when the operating condition changes. do.

As a result, as shown in Fig. 5(b), the amount of ammonia gas injected increases by a predetermined amount prior to the change in the NOx concentration at the inlet of the denitrification reactor. In a coal-fired boiler, for example, in the case of a pressurized mill, the operating state is determined at the time of startup, such as when the coal feeder is started, and during the shutdown process, when the hot air to the mill is cut off. Notice that the NOx concentration suddenly changes at the time of change,
When the operating conditions change as described above, the control signal is corrected by adding a correction signal that matches the amount of change in the NOx concentration value at the inlet of the denitrification reactor predicted in advance for a predetermined period of time when the fluctuation settles down. It is possible to provide a denitrification device having features such as being able to maintain a constant NOx concentration at the outlet of the denitrification device even if conditions change.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can of course be implemented with appropriate modifications within the scope of the gist. It is also possible to set a plurality of optimal signal levels according to the change value of the concentration at the inlet of the denitrification reactor, and to select and output the optimal signal level according to the change in the operating condition R.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of the denitrification equipment, Fig. 2 is a block diagram showing the configuration of a conventional control system in the denitrification equipment,
Figure 3 is a time chart for explaining an example of its operation.
FIG. 4 is a block diagram showing one embodiment of the present invention, and FIG. 5 is a time chart showing an example of its operation. 1... Boiler furnace, 2... Push through ff1t1.3.
... Denitrification reactor, 4... Induced draft fan, 5... Chimney,
6... Duct, 7... Ammonia gas generation equipment, 8
... Ammonia gas injection control valve, 9 ... Ammonia gas injection control device, 41 ... NOx concentration transmitter, 42
...supply air amount transmitter, 43.46...multiplier, 4
4... Ammonia gas amount transmitter, 45... Molar ratio calculator, 47... Subtractor, 48... 1lJill device,
49... Correction signal generator, 50... Relay, 51.
...Adder. Applicant Sub-Agent Patent Attorney Takehiko Suzue

Claims (1)

[Claims] In a denitrification device that denitrates nitrogen oxides contained in the exhaust gas of a boiler by reacting them with injected ammonia gas, a means for obtaining the amount of nitrogen oxides in the exhaust gas at the inlet of the denitrification device, and a means for obtaining the amount of nitrogen oxides in the exhaust gas at the inlet of the denitrification device, means for calculating the required ammonia gas amount from the oxide amount; means for determining the deviation between the required ammonia gas amount and the injected ammonia gas amount; and generating a control output for the injected ammonia gas amount in accordance with this deviation; and means for correcting the amount of nitrogen oxides by providing a correction output for a predetermined period of time in response to a change in the operating state of the denitrification apparatus in accordance with the denitrification reaction delay characteristic of the denitrification apparatus.