CN112206640B - System and method for detecting pH value and concentration of limestone slurry in flying manner, control system and desulfurization system - Google Patents

Abstract

The invention discloses a detection system, method, control system and desulfurization system for limestone slurry pH value concentration soaring. The detection system includes a first-order inertial module, a second-first-order inertial module, a measurement deviation module and a high-low alarm module; The first-order inertial module performs the first filtering on the pH value measurement signal to obtain the first filtered value; the second first-order inertial module performs the second filtering on the pH value measurement signal to obtain the second filtered value; the measurement deviation module combines the first filtered value and the The second filter value is subjected to deviation processing to obtain a deviation value; the high-low alarm module obtains the change trend and change amount of the pH value from the deviation value, performs a threshold value judgment on the change amount, and outputs the detection result of flying up. The present invention uses the real-time pH value signal itself to determine that the pH value signal is in the soaring state, the current distorted signal can be eliminated, and the desulfurization control system can use the soaring detection and judgment signal to process the real-time pH value signal.

Description

Limestone slurry pH concentration detection system, method, control system and desulfurization system

technical field

The invention relates to the field of FGD desulfurization automatic control of coal-fired power plants, in particular to a limestone slurry pH value concentration soaring detection system, method, control system and desulfurization system.

Background technique

Sulfur dioxide (SO ₂ ) mainly comes from the combustion process of coal, oil and natural gas, and is one of the main air pollutants. Therefore, controlling SO ₂ emissions from coal-fired power plants is one of the main measures to reduce SO ₂ content in the atmosphere.

According to the "Emission Standard of Air Pollutants for Thermal Power Plants" (GB13223-2011), in order to reduce the total amount of pollutants emitted by coal-fired power plants, each coal-fired power plant will align the pollutant emission standards of coal-fired power plants with the "gas turbine emission standards", namely: soot The three emission limits of , sulfur dioxide and nitrogen oxides are 5mg/Nm3, 35mg/Nm3 and 50mg/Nm3 respectively, which are usually defined as the "ultra-clean emission" standard of coal-fired boilers in the industry.

There are many ways to reduce SO ₂ emissions. Currently commonly used SO2 control technologies are basically divided into _three categories: "Desulfurization before combustion, Desulfurization during combustion and Desulfurization after combustion, namely Flue Gas Desulfurization (FGD).

Pre-combustion desulfurization refers to the washing of raw coal by physical or chemical methods to remove or reduce impurities such as sulfur and ash in the raw coal. The methods used include coal preparation, gasification, coal-water slurry and briquette processing. However, this method can only remove part of the sulfur (mainly inorganic sulfur) in the coal, and cannot fundamentally solve the problem of SO ₂ pollution to the atmosphere; the desulfurization during combustion is to inject lime CaO/CaCO ₃ absorbent into the furnace to solidify S0 ₂ /SO ₃ is used for desulfurization. The methods used include calcium injection in the furnace and limestone mixing in fluidized bed for desulfurization; post-combustion desulfurization, namely flue gas desulfurization (FGD), refers to the addition of desulfurization equipment to the flue at the tail of the boiler, and the use of desulfurization agents. Desulfurization of flue gas, including wet and dry (semi-dry) desulfurization processes. Among them: Limestone-gypsum wet method is considered to be the most effective way to control SO ₂ emissions.

The existing desulfurization control system takes the SO ₂ concentration at the net flue gas outlet of the coal-fired generator set as the control target, and controls the pH value concentration of the limestone slurry in the limestone-gypsum wet desulfurization control, so as to control the degree of SO ₂ absorption, thereby controlling the pH value of the limestone slurry. The SO ₂ concentration at the net flue gas outlet meets the requirements of environmental protection.

In the existing desulfurization control system, the pH concentration of limestone slurry needs to be used to calculate the required valve opening of the limestone slurry, so as to realize the control of SO ₂ content in the net flue gas outlet after desulfurization.

From the analysis of operation status and control logic: FGD desulfurization control system automatically put into operation depends on the determination of pH concentration of limestone slurry.

Due to the regular cleaning of the limestone slurry pH concentration measuring device (cleaning once every hour), the pH value concentration of limestone slurry loses its authenticity, and the control system cannot correctly obtain the cleaning process, and the measured value rises greatly, which affects the measurement of limestone slurry pH concentration. Accuracy, resulting in automatic desulfurization control can not adapt to pH changes and put into automatic.

SUMMARY OF THE INVENTION

In order to solve the problem of signal distortion caused by the sharp rise of pH value in cleaning, the present invention provides a detection system, method, control system and desulfurization system of limestone slurry pH value concentration fly-up. The invention can ensure the normal operation of the PID of the desulfurization control system after removing the distorted signal from the real-time pH value signal.

To achieve the above object, the present invention adopts the following technical solutions to realize:

A limestone slurry pH value concentration soaring detection system, comprising: a first-order inertial module, a second-first-order inertial module, a measurement deviation module and a high-low alarm module;

The first-order inertial module is used to perform a first filter on the pH value measurement signal to obtain a first filter value;

The second first-order inertial module is used to perform a second filter on the pH value measurement signal to obtain a second filter value;

The measurement deviation module is used to perform deviation processing on the first filter value and the second filter value to obtain a deviation value;

The high and low alarm module is used to obtain the change trend and change amount of the pH value from the deviation value, perform a threshold value judgment on the change amount, and output the detection result of the soaring rise.

As a further improvement of the present invention, the transfer function formula of the first-order inertial module is:

The transfer function formula of the second first-order inertial module is:

Among them, G(s) represents the ratio of the Laplace transform of the input to the output of the linear system response under the zero initial condition; T1, T2 represent the inertial time constant of the inertial link.

As a further improvement of the present invention, the inertia time T1 of the first-order inertial module is 10s-20s; the inertial time T2 of the first-order inertial module is 60s-70s.

As a further improvement of the present invention, it also includes a soaring detection input switch and a soaring detection and input confirmation module;

The soaring detection input switch is used to give the working state of the soaring detection system;

The ascension detection and input confirmation module is used for judging the validity of the ascension detection result according to the ascension detection result and the working state of the ascension detection input switch.

A detection method for a limestone slurry pH value concentration soaring detection system, comprising the following steps:

performing a first filtering on the pH value measurement signal to obtain a first filtering value;

performing a second filter on the pH value measurement signal to obtain a second filter value;

Performing deviation processing on the first filter value and the second filter value to obtain a deviation value;

The change trend and change amount of pH value are obtained from the deviation value, the threshold value is judged for the change amount, and the detection result of the soaring rise is output.

As a further improvement of the present invention, it also includes:

According to the given working status of the ascension detection system and the ascension detection result, the validity of the ascension detection result is judged.

The validity means that when the Feisheng detection input switch is in the input state, and the high and low alarm module output Feisheng detection result is true, the output of Feisheng detection control system is true; otherwise, the signal that detects the pH value is in the Feisheng state, and the signal is distorted. .

An FGD desulfurization automatic control system, comprising a pH value measurement system, a desulfurization control system and the limestone slurry pH value concentration soaring detection system;

The pH value measurement system is connected to the pH value measurement device for obtaining a pH value measurement signal;

The described limestone slurry pH value concentration soaring detection system is used for judging whether the pH value measurement signal obtained by the pH value measuring device is in soaring distortion;

The desulfurization control system is used to control the SO ₂ absorbent according to the result of the fly-up distortion.

An FGD desulfurization system includes a boiler descending heat exchanger, a denitration ammonia injection grill, a denitration reactor, an air preheater, an electrostatic precipitator, a desulfurization absorption tower, a chimney, a limestone slurry circulating pump, a pH value measuring device, a limestone New slurry replenishment pipeline and described FGD desulfurization automatic control system;

The flue gas from the boiler combustion passes through the heat exchanger in the descending section of the boiler to reach the denitrification and ammonia injection grille, and then mixes with the injected ammonia-air mixture, and enters the denitration reactor for chemical reaction and denitrification. After the heat is recovered by the heater, it is discharged into the atmosphere through the chimney through the electrostatic precipitator and the desulfurization absorption tower;

The limestone slurry circulating pump is connected to the spray equipment in the desulfurization absorption tower for limestone slurry supply; the pH value measuring device is arranged in the limestone slurry in the desulfurization absorption tower, and the pH value measuring device is electrically connected to the FGD desulfurization automatic control system. connection; the new limestone slurry supplement pipeline is communicated with the desulfurization absorption tower, and the FGD desulfurization automatic control system controls the on-off of the new limestone slurry supplement pipeline.

As a further improvement of the present invention, the chimney is also provided with a net flue gas SO ₂ measuring device.

Compared with the prior art, the pH value soaring detection system provided by the present invention can automatically identify and eliminate the false and distorted signals of the pH value that are useless to the desulfurization control system and even interfere with the desulfurization control system, laying a foundation for the desulfurization control system to be fully automatic in real time. .

The invention adopts two first-order inertial modules to filter and process the pH value measurement signal, and performs deviation processing, performs threshold value judgment on the change amount, and outputs the detection result of flying liters, and judges whether the pH value signal is distorted by the real-time pH value signal itself. Solve the problem that the pH value is unavailable due to the cleaning of the pH value measuring device. Because the pH value measuring device is cleaned regularly, the desulfurization control system cannot obtain the cleaning information of the pH value measuring device, and the pH value measurement signal will rise when the pH value measuring device is cleaned, the signal will be distorted, and the signal cannot be used by the desulfurization control system. The measured value changes greatly, which affects the measurement accuracy and corresponding time, which in turn affects the input of the desulfurization control system and affects the environmental protection indicators controlled by the desulfurization system. The present invention uses the real-time pH value signal itself to judge that the pH value signal is in the state of soaring, the current distorted signal can be eliminated, and the desulfurization control system can use the soaring detection and judgment signal to process the real-time pH signal. The real-time pH value signal can ensure the normal operation of the PID of the desulfurization control system after eliminating the distorted signal.

Description of drawings

Fig. 1 is the block diagram of pH value soaring detection system;

Fig. 2 is the schematic diagram of pH value measurement Femtoliter detection system;

Fig. 3 is the flow chart of desulfurization system;

Device and module code description table in the figure:

1. Heat exchanger in the descending section of the boiler;

2. Denitrification and ammonia injection grill;

3. Denitrification reactor;

4. Air preheater;

5. Electrostatic precipitator;

6. Desulfurization absorption tower;

7. Chimney;

8. Net flue gas SO ₂ measuring device;

9. Limestone slurry circulating pump;

10. Limestone slurry pH value measuring device;

11. Limestone new slurry supplement pipeline;

12. LAG first-order inertial module;

13. LAG second-order inertial module;

ON/OFF, Feisheng detection input switch module;

ALARM, high and low alarm module;

DEV, measurement deviation module;

AND, Feisheng detection and input confirmation module.

Detailed ways

In order to make those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only The embodiments are part of the present invention, not all of the embodiments, and are not intended to limit the scope of the present disclosure. Furthermore, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Various structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. The figures are not to scale, some details have been exaggerated for clarity, and some details may have been omitted. The shapes of various regions and layers shown in the figures and their relative sizes and positional relationships are only exemplary, and in practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art should Regions/layers with different shapes, sizes, relative positions can be additionally designed as desired.

In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present therebetween. element. In addition, if a layer/element is "on" another layer/element in one orientation, then when the orientation is reversed, the layer/element can be "under" the other layer/element.

It should be noted that the terms "first", "second" and the like in the description and claims of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used may be interchanged under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having" and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those expressly listed Rather, those steps or units may include other steps or units not expressly listed or inherent to these processes, methods, products or devices.

In view of the above problems, in order to solve the problem of FGD desulfurization control, the desulfurization control cannot be put into operation due to the signal distortion of the limestone slurry pH value measuring device due to the sharp rise of the cleaning pH value.

The first object of the present invention is to provide a limestone slurry pH concentration soaring detection system, including: a first-order inertial module 12, a second-first-order inertial module 13, a measurement deviation module DEV and a high-low alarm module ALARM;

The first-order inertial module 12 is used to perform a first filter on the pH value measurement signal to obtain a first filter value;

The second first-order inertial module 13 is used to perform a second filter on the pH value measurement signal to obtain a second filter value;

The measurement deviation module DEV is configured to perform deviation processing on the first filter value and the second filter value to obtain a deviation value;

The high and low alarm module ALARM is used to obtain the change trend and change amount of the pH value from the deviation value, perform threshold value judgment on the change amount, and output the detection result of soaring.

The limestone slurry pH value concentration fly-up detection system is located in the DCS, between the pH value measurement system and the desulfurization control system. See Figures 1 and 2.

The pH value measurement signal soaring detection system includes two links: pH value deviation processing and pH value alarming, namely the first and first-order inertial module 12, the second and first-order inertial module 13, the measurement deviation module DEV, the high and low alarm module ALARM, and the soaring detection input The switch ON/OFF and the ascension detection input confirmation module AND constitute the ascension detection control system. The above are all the key components used in the desulfurization control of the fly-up detection and control system proposed by the present invention.

The composition of the pH value soaring detection and control system proposed by the present invention is shown in Figure 1. The pH value measurement in the desulfurization absorption tower obtains the pH value measurement signal through the measuring device, and sends it to the desulfurization control system for desulfurization control after processing in the measurement process.

The transfer function formula of the first-order inertial module 12 is:

The transfer function formula of the second first-order inertial module 13 is:

Among them, G(s) represents the ratio of the Laplace transform of the input to the output of the linear system response under the zero initial condition; T1, T2 represent the inertial time constant of the inertial link.

The pH value measurement signal enters the first-order inertial module 12, and the inertial module inertia time is between 10s and 20s; the pH value measurement signal enters the second first-order inertial module 13, and the inertial module inertial time is between 60s and 70s.

The output of the first-order inertial module 12 and the output of the second-order inertial module 13 enter the measurement deviation module DEV; the output of the measurement deviation module DEV enters the high-low alarm module ALARM, and the high-low alarm module ALARM detects the change trend and change of the current pH value Once it exceeds the preset threshold, the high and low alarm module ALARM outputs the soaring detection result. The result of the ascension detection and the ON/OFF state of the ascension detection input switch enter the ascension detection input confirmation module AND.

The second object of the present invention is to provide a kind of detection method of limestone slurry pH value concentration soaring detection system, comprising the following steps:

performing a first filtering on the pH value measurement signal to obtain a first filtering value;

performing a second filter on the pH value measurement signal to obtain a second filter value;

Performing deviation processing on the first filter value and the second filter value to obtain a deviation value;

The change trend and change amount of pH value are obtained from the deviation value, the threshold value is judged for the change amount, and the detection result of the soaring rise is output.

When the soaring detection input switch ON/OFF is in the input state, and the high and low alarm module ALARM outputs the soaring detection result is true, the output of the soaring detection control system is true. Otherwise, at this time, the signal that detects the pH value is in a soaring state, and the signal is distorted and unavailable.

The third object of the present invention is to provide a FGD desulfurization automatic control system, including a pH value measurement system, a desulfurization control system and the limestone slurry pH value concentration soaring detection system;

The pH value measurement system is connected to the pH value measurement device for obtaining a pH value measurement signal;

The described limestone slurry pH value concentration soaring detection system is used for judging whether the pH value measurement signal obtained by the pH value measuring device is in soaring distortion;

The desulfurization control system is used to control the SO ₂ absorbent according to the result of the fly-up distortion.

The pH value soaring detection control system is located between the pH value measurement system and the desulfurization control system. After the pH value measurement signal is sent from the measurement system, before entering the desulfurization control, it enters the Feisheng detection control system. The soaring detection and control system detects the pH value measurement signal online in real time. Once the pH value measurement signal is detected to be soaring due to the cleaning of the measuring instrument, the signal is distorted, and the distorted pH value measurement signal will not be sent to the desulfurization control system.

The limestone slurry pH value concentration Feather detection system works when desulfurization control is put into automatic operation, and the pH value measurement Feather detection system generates a Feather judgment signal of the pH value measurement signal. When the pH value measurement soaring detection system determines that the measurement signal is in the soaring state, the pH value signal entering the desulfurization control is in a distorted state, and the distorted signal will be eliminated.

The function of the limestone slurry pH concentration detection system is to judge whether the pH value measurement device is distorted due to cleaning, so as to judge whether the pH value measurement signal is in the fly-up distortion. The system consists of two links: pH value deviation processing module and pH value deviation alarm module. The system generates a reasonable pH value signal distortion judgment signal for the control of the desulfurization system to ensure a reasonable desulfurization control quality and prevent the desulfurization control system from fluctuating greatly.

The fourth object of the present invention is to provide a FGD desulfurization system, which includes a boiler descending section heat exchanger 1, a denitration ammonia spray grid 2, a denitration reactor 3, an air preheater 4, an electric precipitator 5, and a desulfurization absorption tower 6 , chimney 7, limestone slurry circulating pump 9, pH value measuring device 10, new limestone slurry supplement pipeline 11 and described FGD desulfurization automatic control system;

A typical process of the desulfurization system is shown in Figure 3. The flue gas from the boiler combustion passes through the boiler descending section heat exchanger 1, reaches the denitration ammonia injection grid 2, is mixed with the injected ammonia-air mixture, and enters the denitration reactor 3. The chemical reaction is carried out, and the denitrified flue gas enters the air preheater 4 for further heat recovery, passes through the electrostatic precipitator 5 and the desulfurization absorption tower 6, and then is discharged into the atmosphere through the chimney 7.

In the desulfurization absorption tower 6, the limestone slurry is supplied by the limestone slurry circulation pump 9 for the spraying equipment of the absorption tower. The limestone slurry reacts with the SO ₂ in the original flue gas and is absorbed to remove most of the SO ₂ . The limestone concentration of the limestone slurry is detected by the pH value measuring device 10 and sent to the desulfurization control system of DCS for use. When the pH value of the limestone slurry is high, it means that the absorbent for absorbing SO ₂ in the limestone slurry is insufficient, and it will be supplemented through the new limestone slurry supplement pipeline 11 .

The limestone slurry circulating pump 9 is connected with the limestone slurry for the spray equipment in the desulfurization absorption tower 6; the pH value measuring device 10 is arranged in the limestone slurry in the desulfurization absorption tower 6, and the pH value measuring device 10 is connected with the FGD. The desulfurization automatic control system is electrically connected; the new limestone slurry supplement pipeline 11 is connected with the desulfurization absorption tower 6 , and the FGD desulfurization automatic control system controls the on-off of the limestone new slurry supplement pipeline 11 . The chimney 7 is also provided with a clean flue gas SO ₂ measuring device 8 .

The design method of the pH value measurement signal soaring detection system: the pH value signal enters the DCS through the measuring signal system, and passes through the pH value signal soaring detection system before being sent to the desulfurization control system. The soaring detection system detects the current pH value measurement signal online in real time. When the soaring trend is detected and the current pH value is judged to be in the soaring state, the current pH value signal is not adopted, and the value before the soaring is used as the pH value control amount. sent to the desulfurization control system.

For example: the DEV module of the pH value signal soaring detection system detects the deviation of the first-order inertial module 12 and the second-order inertial module 13 in real time; Threshold, according to field experience, the high alarm judgment value is set between 8 and 10; the low alarm judgment value is set between -8 and -10) The diagnostic result information of the output signal soaring.

The main features of this technical solution are:

1. Use the real-time pH signal itself to judge whether the pH signal is distorted, and solve the problem of unusable pH caused by the cleaning of the pH measuring device. Because the pH value measuring device is cleaned regularly, the desulfurization control system cannot obtain the cleaning information of the pH value measuring device, and the pH value measurement signal will rise when the pH value measuring device is cleaned, the signal will be distorted, and the signal cannot be used by the desulfurization control system. The measured value changes greatly, which affects the measurement accuracy and corresponding time, which in turn affects the input of the desulfurization control system and affects the environmental protection indicators controlled by the desulfurization system.

2. When the real-time pH signal itself is used to judge that the pH signal is in the soaring state, the current distorted signal can be eliminated, and the desulfurization control system can use the soaring detection and judgment signal to process the real-time pH signal. The real-time pH value signal can ensure the normal operation of the PID of the desulfurization control system after eliminating the distorted signal.

3. When the real-time pH value signal is used to judge that the pH value signal is in the soaring state, the limestone slurry supply valve can be accurately controlled to prevent the valve from exiting the automatic operation state due to the distortion of the pH value signal, and the desulfurization control system can run stably .

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any modification made on the basis of the technical solution proposed in accordance with the technical idea of the present invention falls within the scope of the claims of the present invention. within the scope of protection.

Claims (5)

1. The utility model provides a lime stone thick liquid pH value concentration fly-lift detecting system which characterized in that includes: the system comprises a first-order inertia module (12), a second-order inertia module (13), a measurement deviation module (DEV) and an ALARM module (ALARM);

the first order inertia module (12) is used for carrying out first filtering on the pH value measurement signal to obtain a first filtering value;

the second first-order inertia module (13) is used for carrying out second filtering on the pH value measurement signal to obtain a second filtering value;

the deviation measuring module (DEV) is used for carrying out deviation processing on the first filtering value and the second filtering value to obtain a deviation value;

the high-low ALARM module (ALARM) is used for obtaining the change trend and the change quantity of the pH value according to the deviation value, carrying out threshold judgment on the change quantity and outputting a flight-rise detection result;

the first-order inertia module (12) and the second first-order inertia module (13) are arranged in parallel;

the transfer function formula of the first order inertia module (12) is as follows:

；

the transfer function formula of the second first order inertia module (13) is as follows:

；

wherein G(s) characterizes the ratio of the Laplace transform of the linear system response input and output at zero initial condition; t1 and T2 represent inertia time of the inertia link;

the inertia time T1 of the first-order inertia module (12) is 10 s-20 s; the inertia time T2 of the first-order inertia module (12) is 60 s-70 s;

the system also comprises a flying detection input switch (ON/OFF) AND a flying detection input confirmation module (AND);

the flying detection input switch (ON/OFF) is used for providing the working state of the flying detection system;

AND the flying detection input confirmation module (AND) is used for judging the validity of the flying detection result according to the flying detection result AND the working state of a flying detection input switch (ON/OFF).

2. A detection method of a limestone slurry pH value concentration fly-up detection system is based on the limestone slurry pH value concentration fly-up detection system of claim 1, and is characterized by comprising the following steps:

carrying out first filtering on the pH value measurement signal to obtain a first filtered value;

carrying out second filtering on the pH value measurement signal to obtain a second filtering value;

carrying out deviation processing on the first filtering value and the second filtering value to obtain a deviation value;

obtaining the change trend and the change quantity of the pH value according to the deviation value, carrying out threshold judgment on the change quantity, and outputting a fly-up detection result;

further comprising:

judging the validity of the fly-lift detection result according to the working state of the fly-lift detection system and the fly-lift detection result;

the validity means that when a flying lift detection switch (ON/OFF) is in a switching state and a high-low ALARM module (ALARM) outputs a flying lift detection result to be true, the output of a flying lift detection control system is true; otherwise, the signal for detecting the pH value is in a flying state, and the signal is distorted.

3. An automatic FGD desulfurization control system, which is characterized by comprising a pH value measuring system, a desulfurization control system and a limestone slurry pH value concentration fly-up detection system of claim 1;

the pH value measuring system is connected with the pH value measuring device and is used for obtaining a pH value measuring signal;

the limestone slurry pH value concentration fly-up detection system is used for judging whether a pH value measurement signal obtained by the pH value measurement device is in fly-up distortion or not;

the desulfurization control system is used for controlling SO according to the fly-up distortion result ₂ The absorbent is controlled.

4. An FGD desulfurization system is characterized by comprising a boiler descending section heat exchanger (1), a denitration ammonia-spraying grid (2), a denitration reactor (3), an air preheater (4), an electric dust remover (5), a desulfurization absorption tower (6), a chimney (7), a limestone slurry circulating pump (9), a pH value measuring device (10), a limestone new slurry supplementing pipeline (11) and the FGD desulfurization automatic control system of claim 3;

flue gas combusted by the boiler flows through the boiler descending section heat exchanger (1) to reach the denitration ammonia injection grid (2), then is mixed with an injected ammonia-air mixture, enters the denitration reactor (3) for chemical reaction denitration, enters the air preheater (4) for recovering heat, passes through the electric dust collector (5) and the desulfurization absorption tower (6), and is discharged into the atmosphere through the chimney (7);

the limestone slurry circulating pump (9) is connected with spraying equipment in the limestone slurry supply desulfurization absorption tower (6); the pH value measuring device (10) is arranged in limestone slurry in the desulfurization absorption tower (6), and the pH value measuring device (10) is electrically connected with an FGD desulfurization automatic control system; the limestone new slurry supplementing pipeline (11) is communicated with the desulfurization absorption tower (6), and the FGD desulfurization automatic control system controls the on-off of the limestone new slurry supplementing pipeline (11).

5. A FGD desulfurization system according to claim 4, characterized in that the stack (7) is further provided with clean flue gas SO ₂ A measuring device (8).

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