JPS5955334A - System for controlling injection of reducing agent in denitrator for stack gas - Google Patents

Abstract

PURPOSE:To provide both performances of control for maintaining a specified denitration reduction ratio and control for maintaining specified NOx in the inlet of a chimney and to enable automatic changing over of both by adding the control signal for maintaining the specified NOx value in the inlet of the chimney to the signal from a reduction ratio setter. CONSTITUTION:The total NOx amt. calculated by a multiplier 11 from the output signals of a signal transmitter 9 for the flow rate of air for combustion and a detector for NOx in the gas at the outlet of a fuel economizer and the signal from a reduction ratio setter 13 are calculated with a multiplier 12, and the output thereof is used as a demand signal for the amt. of gaseous NH3 for denitration in controlling NOx at the specified denitration reduction ratio. On the other hand, the signal of a detector 24 for NOx at the inlet of a chimney and the set signal of the NOx value at the inlet of the chimney are calculated with a calculator 26, and the deviation thereof is inputted through a multiplier 27 which adjusts the gain so as to meet load to a proportional plus integral calculator 28. The output of the calculator 28 is inputted to an adder 28 by which said output is added to the signal from the setter 13 and is converted to the set value for specified denitration reduction ratio from optional partial load, whereby the control for maintaining the specified NOx value at the inlet of the chimney is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flue gas denitrification device, and particularly to a flue gas denitrification device equipped with a reducing agent injection amount control valve and suitable for reducing nitrogen oxides (hereinafter referred to as NOx) in flue gas. The present invention relates to a reducing agent injection control system.

Conventionally, the basic control method for NOx in flue gas denitrification equipment is to multiply the total amount of NOx, which is calculated by "exhaust gas flow rate" x "NOx value at the exit of the economizer," by the reduction ratio (so-called molar ratio). For example, a deviation calculation (or ratio calculation) is performed between the ammonia gas injection amount request signal and the feedback signal of the actual ammonia gas injection amount, and the ammonia gas injection amount is controlled by the proportional-integral calculation signal of this deviation. This method is commonly used. This is U
This method attempts to maintain a predetermined denitrification performance over the entire load range by always measuring the amount of ammonia gas injected at a constant reduction ratio with respect to the total amount of NOx in one scum.

However, recently, in addition to this method of constantly maintaining the denitrification performance at a constant level, attempts have been made to detect and feed back the NOx value at the smoke inlet to control the NOx value at the smoke inlet to a predetermined value that matches the environmental regulation value. The so-called smoke inlet NO.
The number of systems that perform constant x control is increasing. The above purpose is to achieve economical operation by suppressing the amount of ammonia gas injection at partial loads by constantly maintaining the NOx value at the smoke inlet, which is the final purpose of the denitrification equipment, at a predetermined value in accordance with environmental regulations. It is. As described above, there are three conventional methods as described above, and one of these methods is currently employed.

Hereinafter, a conventional NOx control system will be explained with reference to FIGS. 1 to 3. FIG. 1 is a flow explanatory diagram of the denitrification device, and FIG. 2 is a NOx control system diagram with a constant denitrification and reduction ratio. In FIG. 1, exhaust gas from a boiler 1 passes through a economizer 2 and is introduced into a denitrification reactor 3.

-M The denitrified ammonia gas for death is injected into the denitrification reactor 3 through the denitrified ammonia gas amount control valve 4. The exhaust gas that has been reduced in the denitrification reactor 3 is led to the chimney and released into the atmosphere. On the other hand, the combustion air is forced draft a
(hereinafter referred to as FDP) 7, the air passes through an air preheater 8 and is guided to the boiler 1.

The exhaust gas NOx at the outlet of the economizer 2 is the exhaust gas NOx at the outlet of the economizer 2.
The amount of ammonia gas injected into the denitrification reactor 3 is determined by the x detector 6, and the amount of ammonia gas injected into the denitrification reactor 3 is determined by the ammonia gas flow rate transmitter 5, and the combustion air flow rate is changed to the exhaust gas flow rate by a function generator 10 (not shown). The air flow rate is detected by the combustion air flow rate transmitter 9, and the smoke inlet NOx is detected by the smoke inlet NOx detector 24. One of the basic control methods of conventional NOx control, the control to keep the denitration reduction ratio (molar ratio) constant is the product of the process gas flow rate (converted from the combustion air flow) and the NOx value at the exit of the economizer. The aim is to achieve a predetermined denitrification effect over the entire load range by injecting an amount of ammonia gas as a reducing agent at a constant reduction ratio with respect to the total amount of NOx.

Next, with reference to FIG. 2, a NOx control system with a constant denitrification/reduction ratio among conventional control systems will be explained. The signal from the combustion air flow rate transmitter 9 is converted into a processing gas flow rate by the function generator 10 and input to a multiplier 11 . One of the economizer outlet NOx value signals is transmitted from the economizer outlet gas NOx detector 6 and input to the multiplier 11, and the "processed gas flow rate" x "the economizer outlet NOx value" = "total amount of NOx" Calculated. The total amount of NOx is input to the multiplier 12, where it is multiplied by the reduction ratio (molar ratio) given by the reduction ratio setting device 13 to obtain a denitrification ammonia gas amount request signal, and the request signal is input to the multiplier 12. Adder 31 to connect
Enter. On the other hand, a differentiator 2 is connected to the output terminal of the multiplier 11.
0 is connected, and after detecting that the total amount of NOx has changed due to load fluctuation, the output signal is amplified by the gain adjuster 21, the upper and lower limits are limited by the signal limiter 22, and the change rate limiter 23 After limiting the signal change rate by , this is input to the adder 31 , added to the limited denitrification ammonia gas amount request signal, and input to the deviation calculator 14 . The signal from the ammonia gas flow rate transmitter 5 is input as a feedback signal to the deviation calculator 14, and the above two deviation calculation results are input to the proportional-integral calculator 15, and the proportional-integral calculation output is the denitrified ammonia gas The signal becomes an opening command signal for the amount adjusting valve 4, passes through the adder 17 and the switch 18, and drives the denitrified ammonia gas amount adjusting valve 4. The adder 17 is used together with the function generator 16 to regulate the opening degree of the denitrified ammonia gas amount control valve 4 as a predetermined +SFJ degree signal based on the denitrified ammonia gas amount request signal from the multiplier 12. Further, the switching device J8 is an automatic or manual switching device,
When manually operating the denitrification ammonia gas amount control valve 4, the denitrification ammonia gas amount control valve 4 is operated in response to a signal from the signal generator 19. In the above method, when the total amount of NOx suddenly changes when the load fluctuates, in order to prevent the denitrification performance from temporarily decreasing due to a time delay in the reduction reaction between NOx and ammonia gas in the denitrification reactor 3, the nominal amount is reduced when the load increases. In addition, when the square cargo is lowered, the ammonia sludge is adjusted to a small level in order to maintain the denitrification performance during load fluctuations. This control method attempts to maintain the denitrification performance by keeping the reduction ratio constant at all times, and the NOx value at the smoke inlet, which is the final objective of the denitrification device, is given only as a result of this control.

As another method of the conventional control method, there is a control method as shown in FIG. 3, which attempts to maintain the NOx value at the smoke inlet, which is the control target or ultimate goal of the denitrification device, at a constant value according to environmental regulations. In this method, in FIG. 3, the signal of the smoke inlet No The calculation is performed and the output thereof is input to the multiplier 27. The multiplier 27 is
The function generator 10 is connected to the multiplier 12 through a signal line different from the signal line shown in the conventional example of FIG. The configuration up to inputting information is replaced with the return ratio setting device 13 in the conventional example shown in FIG. 2 above, and other grooves are the same as those in FIG. 2 above.

As mentioned above, the conventional one-way control system employs either NOx control that keeps the denitrification/reduction ratio constant or NOx control that keeps the NOx value at the smoke inlet constant. In other words, it is possible to maintain the planned performance of the denitrification equipment at a constant level at all times, and in the low load range, the NOx value at the smoke inlet is not lowered more than necessary, thereby meeting the environmental regulations. There has been a demand for the development of a control system that can control the amount of denitrified ammonia gas to be controlled to a specified value and economically operate the amount of denitrified ammonia gas.

The purpose of the present invention is to meet the above demands and provide a reducing agent injection control system for flue gas denitrification equipment that combines the performance of the three systems described above and that can automatically and continuously switch between the two at any partial load. is to provide.

In short, this invention is based on the basics of NOx control #r+I, 1
The following method is one of the methods, namely, the total amount of NOx (
The deviation between the required amount of ammonia gas and the actual amount of ammonia gas injected is calculated by multiplying the denitrification reduction ratio (molar ratio) by "processed gas miscarriage" x [NOx value output from the economizer] and the actual amount of ammonia gas injected. In the NOx control method, which calculates the amount of ammonia gas to be injected using the calculated output signal, we focused on the setting circuit for the denitration reduction ratio (molar ratio). This method automatically lowers the reduction ratio from a partial load to control the smoke inlet NOx value to the specified value according to environmental regulations in a low load range without lowering it more than necessary. An adder 29 is inserted into the ratio setting signal circuit, and in the adder 29, the smoke entry point N0xI11! The calculated output signal is the proportional integral calculation of the deviation between the feedback signal and its set value, that is, the smoke inlet N0XIii! Input a constant control signal and add it to the signal from the reduction ratio setting device 13 to automatically and continuously change the NOx control with a constant reduction ratio at any partial load to the control with a constant NOX1 direct control at the smoke inlet; Conversely, it is possible to shift from control with a constant chimney population NoX (Fi) to NOx control with a constant reduction ratio.

Hereinafter, this invention will be explained based on the drawings, which has the control functions for both of the above-mentioned conventional needs and can automatically switch between the two at one or any partial load. . FIG. 4 shows a collateral system diagram of one embodiment of the present invention. In the drawings, the same or equivalent parts as in FIGS. 1 to 3 are given the same reference numerals. First, the configuration will be described only with respect to the points that differ from the conventional example shown in FIG. Connect the monitor relay 30, connect the monitor relay 30 to the proportional-integral calculator 28, and read the proportional-integral calculator 28.
Next, the effect will be explained. The total amount of NOx at the inlet of the denitrification device is converted by the function generator 10 from the output signal of the combustion air flow rate generator 9, and the processing gas flow rate is converted by the NOx value from the economizer outlet gas NOx generator 6 in the multiplier 11. The multiplication is calculated and input to the multiplier 12. The denitrification and reduction ratio with respect to the total amount of NOx is determined through an adder 29 based on a signal from the reduction ratio setting device 13. The output of the multiplier 12 is used as a denitrification ammonia gas amount request signal to perform NOx control with a constant denitrification and reduction ratio. On the other hand, the adder 29 provided in the signal line from the denitration reduction ratio setting signal circuit, that is, the reduction ratio setting device 13, receives the signal from the smoke inlet NOx value constant control circuit, that is, the signal from the smoke inlet NOx detector 24. It is input to the deviation calculator 26, and the deviation is calculated by the deviation calculator 26 together with the smoke inlet NOx value setting signal given from the signal setting device 25, and the gain is adjusted (converted to NOx deviation amount) according to the load. The signal is inputted to a proportional-integral calculator 28 via a multiplier 27. A control signal is inputted to the adder 29 to set No. input and add it, directly change the denitrification reduction ratio constant setting from any partial load, generate a smoke inlet NOx value constant control signal, and use this in the multiplier 12 to set the NOx value constant.
This signal is multiplied by the total amount of Ox and used as a denitrification ammonia gas amount request signal to achieve constant control of the smoke inlet NO4.

As explained above, according to the present invention, it is possible to have both NOx control using a constant denitrification reduction ratio and constant NOx value control at the smoke inlet, and to automatically switch between the two depending on an arbitrary partial load. You can get the effect that you can.

[Brief explanation of the drawing]

Figure 1 is a flow explanatory diagram of the denitrification equipment, Figure 2 is a NOx control system diagram with a constant denitrification/reduction ratio, and Figure 3 is a diagram of the NOx control system with a constant denitrification/reduction ratio.
FIG. 4 shows a control system diagram of an embodiment of the present invention. Explanation of symbols 1...Boiler 2...Coal economizer 3...Denitrification reactor 4...Denitrification ammonia gas amount control valve 5...Ammonia gas a Transmitter 6...Coal economizer outlet Gas NOx detector 7...FDF 8...'Air preheater 9
...Combustion air flow rate transmitter 10...Function generator 11...Multiplier 12...
・Multiplier 13...Return ratio setting device 14...
- Deviation calculator 15... Proportional integral calculator 16...
・Function generator 17...Adder 18...Switcher 19...Signal generator 20...Differentiator
21...Gain adjuster 22...Direct number limiter
23... Change rate limiter 24... Smoke inlet NOx
Detector 25... Signal setter 26... Deviation calculator 27
... Multiplier 28 ... Proportional-integral calculator 29
... Adder 30 ... Monitor relay 31
... Adder Attorney Junnosuke Donakamura Figure 1, Figure 1, Half 2

Claims (1)

[Claims] The basic control method for NOx in flue gas denitrification equipment, that is, N calculated from the NOx value in the gas on the upstream side of the reactor and the flue gas flow rate.
The total amount of Ox is multiplied by the reduction ratio, and the deviation between the product, the reducing agent injection amount request signal, and the feedback signal of the actual reducing agent injection amount is proportionally integrated, and the reducing agent injection amount is controlled by the calculated output. In the reducing agent injection control method of flue gas denitrification equipment, the reducing ratio setting signal is added to the output obtained by proportionally integrating the deviation between the feedback signal of the NOx value in the gas at the reactor outlet and its set value, and the reducing agent is In addition to performing NOx suppression with a constant reduction ratio as the injection amount request signal, the difference between the NOx value detection signal in the gas of reactor output # (q) and the NOx value setting signal in the gas on the reactor outlet side is calculated. , the deviation is proportionally integrated, and the reduction ratio setting signal is added to this to generate a constant NOx value control signal in the gas on the reactor outlet side, and this is multiplied by the total amount of Nox to request the reducing agent injection amount. A flue gas denitrification device which controls the NOx value in the gas at the reactor outlet side as a signal and is capable of automatically and continuously switching between the two sub-systems at any given load. reducing agent injection control method.