Power station boiler air heater automatic control system and method based on multi-parameter detection

Abstract

The invention belongs to the technical field of industrial process control. According to the power station boiler air heater automatic control system and method based on multi-parameter detection, multiple kinds of real-time detection data such as the flue gas acid dew point temperature, the SO3 concentration in flue gas and the denitration ammonia escape concentration are introduced into the control system, and an air pre-heater air heater automatic control strategy suitable for all working conditions is constructed. The air pre-heater inlet air temperature set value automatically adapts to the flue gas acid dew point temperature and the air pre-heater outlet smoke temperature real-time change data, dynamic compensation of air pre-heater inlet air temperature control is achieved when the flue gas acid dew point temperature fluctuates, and low-temperature corrosion of the air pre-heater is avoided in time. The logic criterion that ammonium bisulfate solidification occurs at the cold end of the air pre-heater is built, override action of an air heater control system of the air pre-heater is automatically triggered, a steam regulating valve of the air heater is rapidly and fully opened, the comprehensive temperature of the cold end of the air pre-heater is increased, ammonium bisulfate deposition is reduced in time, and air pre-heater blocking is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial process control, and in particular to an automatic control system and method for a boiler air heater of a power station based on multi-parameter detection. Background Art

[0002] The statements in this section merely provide background art related to the present invention and do not necessarily constitute prior art.

[0003] The combustion air (boiler secondary air) of large power station boilers is first heated by steam in the steam heater (air heater) before entering the air preheater (referred to as air preheater). The amount of heating steam is controlled by controlling the steam regulating valve of the air heater to adjust the comprehensive temperature of the cold end of the air preheater (the sum of the air temperature at the inlet of the air preheater and the flue gas temperature at the outlet of the air preheater). The purpose is to ultimately control the wall temperature of the heat transfer element at the cold end of the air preheater to make it higher than the acid dew point temperature of the flue gas, thereby preventing the cold end of the air preheater from low temperature corrosion due to too low temperature.

[0004] However, the inventors found in their research that in the above control scheme, since boilers often burn coals with different sulfur contents, the flue gas acid dew point temperature also changes accordingly. In the conventional control scheme, the acid dew point temperature value is calculated based on an empirical formula, and the authenticity and real-time performance of the calculation result are poor. The heater outlet temperature control cannot automatically adapt to the flue gas acid dew point temperature changes accurately and quickly, and the air preheater cold end wall temperature is controlled to be slightly higher than the actual flue gas acid dew point temperature, which cannot timely and effectively prevent and reduce the low-temperature corrosion of the air preheater; in addition, when the SO3 concentration in the boiler denitrification outlet flue gas is higher than the ammonia escape (NH3) concentration, the reaction between the two will mainly generate ammonium bisulfate (NH4HSO4). According to the physicochemical properties of NH4HSO4, when the flue gas temperature is lower than 147°C, NH4HSO4 is solid, which will aggravate the blockage of the air preheater. Obviously, when the abnormal condition of ammonium bisulfate solidification occurs at the cold end of the air preheater, it is no longer meaningful for the control system to automatically adjust the comprehensive temperature of the cold end of the air preheater according to the flue gas acid dew point temperature. The conventional control scheme of the air preheater heater cannot meet the full operating requirements of the comprehensive temperature of the cold end of the air preheater. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the present invention provides an automatic control system and method for a power station boiler air heater based on multi-parameter detection, introduces a variety of real-time detection data such as flue gas acid dew point temperature, SO3 concentration in flue gas, and denitrification ammonia escape concentration into the control system, and constructs an automatic control strategy for an air preheater heater suitable for all working conditions, which solves the problem that the air preheater heater control in the conventional control scheme cannot accurately and quickly adapt to the change of flue gas acid dew point temperature, and also takes into account the realization that when the abnormal working condition of ammonium bisulfate solidification occurs at the cold end of the air preheater, the air preheater heater control system is automatically triggered to override the action, quickly fully open the heater steam regulating valve, and increase the comprehensive temperature of the cold end of the air preheater, thereby achieving the purpose of timely reducing the deposition of ammonium bisulfate and alleviating the low-temperature corrosion and blockage of the air preheater.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides an automatic control system for a power station boiler air heater based on multi-parameter detection.

[0008] A power station boiler air heater automatic control system based on multi-parameter detection, comprising: an air preheater inlet air temperature controller, a first function generator, a second function generator, a third function generator, a fourth function generator, a fifth function generator, a sixth function generator, an adder, a differential controller, a filter module, a first high value judgment module, a second high value judgment module, a low value judgment module, a first AND gate logic module, a second AND gate logic module and an analog quantity switching switch;

[0009] The first function generator is used to receive the actual measured value of the flue gas acid dew point temperature and generate the expected wall temperature value of the air preheater cold end, the second function generator is used to receive the actual measured values ​​of the three flue gas temperature measuring points at the air preheater outlet and generate the average value of the flue gas temperature at the air preheater outlet, the third function generator is used to receive the expected wall temperature value of the air preheater cold end and the average value of the flue gas temperature at the air preheater outlet and generate the set value of the air preheater inlet air temperature, the output end of the third function generator is connected to the positive input end of the air preheater inlet air temperature controller, the fourth function generator is used to receive the actual measured values ​​of the three air temperature measuring points at the air preheater inlet and generate the average value of the air preheater inlet air temperature, and the output end of the fourth function generator is connected to the negative input end of the air preheater inlet air temperature controller;

[0010] The first high value judgment module is used to receive the actual value of ammonia escape concentration and the upper limit value of ammonia escape concentration, and the output end of the first high value judgment module is connected to the first input end of the first AND gate logic module; the second high value judgment module is used to receive the actual value of sulfur trioxide concentration in the flue gas at the denitration outlet and the actual value of ammonia escape concentration, and the output end of the second high value judgment module is connected to the second input end of the first AND gate logic module;

[0011] The sixth function generator is used to receive the average inlet air temperature of the air preheater and the average outlet flue gas temperature of the air preheater and generate the measured value of the comprehensive cold-end temperature of the air preheater. The low-value judgment module is used to receive the measured value of the comprehensive cold-end temperature of the air preheater at the output end of the sixth function generator and the lower limit value of the ammonium bisulfate solidification temperature. The output end of the low-value judgment module is connected to the first input end of the second AND logic module. The output end of the first AND logic module is connected to the second input end of the second AND logic module. The output end of the second AND logic module is connected to the switching trigger signal input end of the analog quantity switching switch;

[0012] The measured value of the flue gas acid dew point temperature is sequentially input to the adder after passing through the differential controller, the filtering module and the fifth function generator. The output of the air preheater inlet air temperature controller and the output of the fifth function generator are superimposed by the adder and then connected to the first input end of the analog quantity switching switch. The override action setting value of the warm air heater steam regulating valve is connected to the second input end of the analog quantity switching switch. The output end of the analog quantity switching switch is connected to the control end of the secondary air warm air heater steam regulating valve.

[0013] As a further limitation of the first aspect of the present invention, the measured value of the flue gas acid dew point temperature is sequentially passed through the differential controller, the filtering module and the fifth function generator to obtain a feedforward signal for controlling the inlet air temperature of the air preheater, so that the control system responds to the change of the flue gas acid dew point temperature and performs dynamic compensation for the control of the inlet air temperature of the air preheater.

[0014] As a further limitation of the first aspect of the present invention, when the amount of NH4HSO4 generated by the flue gas is small, or when the comprehensive cold-end temperature is higher than the solidification temperature limit value of NH4HSO4, the analog quantity switching switch selects to conduct the command signal after superimposing the output of the air preheater inlet air temperature controller and the feedforward control, and adjusts the secondary air warm air heater steam regulating valve according to the flue gas acid dew point temperature to control the inlet air temperature of the air preheater;

[0015] The small amount of NH4HSO4 generated by the flue gas includes: SO3 concentration < NH3 concentration; or, SO3 concentration > NH3 concentration and NH3 concentration ≤ 3 ppm.

[0016] As a further limitation of the first aspect of the present invention, when the amount of NH4HSO4 generated by the flue gas is large and the comprehensive cold-end temperature is lower than the solidification temperature limit value of NH4HSO4, the analog quantity switching switch selects to conduct the override control and fully opens the warm air heater steam regulating valve;

[0017] The large amount of NH4HSO4 generated by the flue gas includes: SO3 concentration > NH3 concentration > 3 ppm.

[0018] As a further limitation of the first aspect of the present invention, when the cold end comprehensive temperature rises and is higher than the NH4HSO4 solidification temperature limit, or when the amount of NH4HSO4 generated by the flue gas is not much, the system automatically exits the override control mode, and adjusts the secondary air heater steam regulating valve to control the air temperature of the air preheater inlet according to the flue gas acid dew point temperature;

[0019] As a further limitation of the first aspect of the present invention, the first function generator is used to receive the measured value of the flue gas acid dew point temperature, and calculate the expected wall temperature value of the cold end of the air preheater according to the following formula: expected wall temperature = flue gas acid dew point temperature + 2°C;

[0020] The third function generator is used to receive the expected wall temperature value at the cold end of the air preheater and the average flue gas temperature at the air preheater outlet, and calculate the air preheater inlet air temperature setting value according to the following formula: wall temperature = 0.5 (air preheater outlet flue gas temperature + air preheater inlet air temperature) - 5°C;

[0021] The air preheater inlet air temperature controller calculates the deviation between the air preheater inlet air temperature and the set value and outputs the secondary air heater steam regulating valve opening process control command signal.

[0022] As a further limitation of the first aspect of the present invention, the output of the second function generator is designed to be equal to the average of the three measuring point data of the air preheater outlet flue gas temperature, and the average value of the air preheater outlet flue gas temperature is calculated;

[0023] The output of the fourth function generator is designed to be equal to the average of the three measuring points of the air preheater inlet air temperature, and the average air preheater inlet air temperature is calculated;

[0024] The fifth function generator is designed according to a broken line function;

[0025] The output of the sixth function generator is designed to be equal to the average air temperature at the air preheater inlet + the average flue gas temperature at the air preheater outlet.

[0026] As a further limitation of the first aspect of the present invention, the ammonium bisulfate curing temperature limit is preset to 150°C;

[0027] The preset value of ammonia escape concentration limit is 3ppm;

[0028] The heater steam regulating valve override control opening preset value is 100%;

[0029] The filter time of the filter module is set to 2 seconds.

[0030] In a second aspect, the present invention provides a method for automatically controlling a power station boiler air heater based on multi-parameter detection.

[0031] A method for automatically controlling a power station boiler air heater based on multi-parameter detection, using the automatic control system for a power station boiler air heater based on multi-parameter detection described in the first aspect of the present invention, comprises the following processes:

[0032] When the amount of NH4HSO4 generated by the flue gas is small, or when the comprehensive temperature at the cold end is higher than the solidification temperature limit of NH4HSO4, the analog switch selects to conduct the command signal after the superposition of the output of the air preheater inlet air temperature controller and the feedforward control, and adjusts the steam regulating valve of the secondary air preheater according to the acid dew point temperature of the flue gas to control the air preheater inlet air temperature;

[0033] When the amount of NH4HSO4 generated by the flue gas is large and the comprehensive temperature at the cold end is lower than the solidification temperature limit of NH4HSO4, the analog switch selects to conduct the override control and fully opens the steam regulating valve of the air preheater;

[0034] When the comprehensive temperature at the cold end rises and is higher than the solidification temperature limit of NH4HSO4, or when the amount of NH4HSO4 generated by the flue gas is small, the system automatically exits the override control mode, and adjusts the steam regulating valve of the secondary air preheater according to the acid dew point temperature of the flue gas to control the air preheater inlet air temperature;

[0035] During the process of adjusting the steam regulating valve of the secondary air preheater according to the acid dew point temperature of the flue gas to control the air preheater inlet air temperature, when the acid dew point temperature of the flue gas fluctuates, the change amount of the acid dew point temperature of the flue gas is used as the feedforward signal for the control of the air preheater, and dynamic compensation for the control of the air preheater inlet air temperature is carried out;

[0036] Among them, the small amount of NH4HSO4 generated by the flue gas includes: SO3 concentration < NH3 concentration; or, SO3 concentration > NH3 concentration and NH3 concentration ≤ 3 ppm; the large amount of NH4HSO4 generated by the flue gas includes: SO3 concentration > NH3 concentration > 3 ppm.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] 1. The present invention innovatively proposes a control strategy for the air preheater of a power station boiler based on multi-parameter detection. The set value of the air preheater inlet air temperature automatically adapts to the real-time change data of the acid dew point temperature of the flue gas and the outlet flue gas temperature of the air preheater, and the change signal of the acid dew point temperature of the flue gas is used as the feedforward signal of the air preheater inlet air temperature controller. The control system quickly responds to the need for changes in the acid dew point temperature of the flue gas, realizes dynamic compensation for the control of the air preheater inlet air temperature, and timely avoids the occurrence of low-temperature corrosion of the air preheater, solving the problem that the control of the air preheater in the conventional control scheme cannot accurately and quickly adapt to the change of the acid dew point temperature of the flue gas.

[0039] 2. The present invention innovatively proposes a control strategy for a power plant boiler heater based on multi-parameter detection. By comparing the comprehensive real-time temperature of the cold end of the air preheater and the SO3 concentration in the flue gas with the escape concentration of denitrification ammonia, a logical criterion for the solidification of ammonium bisulfate at the cold end of the air preheater is constructed, and the air preheater heater control system override action is automatically triggered. The heater steam regulating valve is quickly fully opened, and the comprehensive temperature of the cold end of the air preheater is timely increased to reduce the deposition of ammonium bisulfate and alleviate the blockage of the air preheater.

[0040] 3. The present invention innovatively proposes an automatic control strategy for a power station boiler air heater based on multi-parameter detection, which is applicable to various boiler control systems DCS (Distributed Control System) or PLC (Programmable Logic Controller), is easy to configure, and has good application prospects.

[0041] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0043] Figure 1 A schematic diagram of a power station boiler air heater control system based on multi-parameter detection provided by the present invention;

[0044] Among them, 1. the first function generator; 2. the second function generator; 3. the third function generator; 4. the air preheater inlet air temperature controller; 5. the fourth function generator; 6. the adder; 7. the differential controller; 8. the filter module; 9. the fifth function generator; 10. the analog quantity switching switch; 11. the first high value judgment module; 12. the first AND gate logic module; 13. the second high value judgment module; 14. the second AND gate logic module; 15. the sixth function generator; 16. the low value judgment module; 17. the secondary air heater steam regulating valve. DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0046] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0047] In this implementation, a control system for a power station boiler air heater based on multi-parameter detection is proposed, including: a first function generator 1, a second function generator 2, a third function generator 3, an air preheater inlet air temperature controller 4, a fourth function generator 5, an adder 6, a differential controller 7, a filter module 8, a fifth function generator 9, an analog quantity switching switch 10, a first high value judgment module 11, a first AND gate logic module 12, a second high value judgment module 13, a second AND gate logic module 14, a sixth function generator 15, a low value judgment module 16 and a secondary air heater steam regulating valve 17;

[0048] The first function generator 1 is used to receive the actual value of the flue gas acid dew point temperature and generate the expected wall temperature value of the cold end of the air preheater;

[0049] The second function generator 2 is used to receive the measured values ​​of the three flue gas temperature measuring points at the air preheater outlet and generate the average value of the flue gas temperature at the air preheater outlet;

[0050] The third function generator 3 is used to receive the expected wall temperature value of the air preheater cold end and the average flue gas temperature at the air preheater outlet and generate the air preheater inlet air temperature setting value, and the output end of the third function generator 3 is connected to the positive input end of the air preheater inlet air temperature controller 4;

[0051] The fourth function generator 5 is used to receive the measured values ​​of the three air temperature measurement points at the air preheater inlet and generate the average value of the air temperature at the air preheater inlet, and the output end of the fourth function generator 5 is connected to the negative input end of the air preheater inlet air temperature controller 4;

[0052] The output end of the air preheater inlet air temperature controller 4 is connected to the first input end of the adder 6;

[0053] The flue gas acid dew point temperature is sequentially passed through the differential controller 7, the filter module 8 and the fifth function generator 9, and is sent to the second input end of the adder 6 as a feedforward signal of the air preheater inlet air temperature controller;

[0054] The first high value judgment module 11 is used to receive the actual value of ammonia (NH3) escape concentration and the upper limit value of ammonia escape concentration, and the output end of the first high value judgment module 11 is connected to the first input end of the first AND gate logic module 12;

[0055] The second high value judgment module 13 is used to receive the actual measured value of SO3 concentration and the actual measured value of ammonia escape concentration in the flue gas at the denitration outlet, and the output end of the second high value judgment module 13 is connected to the second input end of the first AND gate logic module 12;

[0056] The sixth function generator 15 is used to receive the average air temperature at the air preheater inlet and the average flue gas temperature at the air preheater outlet and generate a measured value of the cold end comprehensive temperature of the air preheater;

[0057] The low-value judgment module 16 is used to receive the measured value of the comprehensive temperature at the cold end of the air preheater and the lower limit value of the ammonium bisulfate solidification temperature at the output end of the sixth function 15 generator. The output end of the low-value judgment module 16 is connected to the first input end of the second AND logic module 14. The output end of the first AND logic module 12 is connected to the second input end of the second AND logic module 14. The output end of the second AND logic module 14 is connected to the switching trigger signal input end of the analog quantity switching switch 10;

[0058] The output of the air preheater inlet air temperature controller 4 and the output of the fifth function generator 9 are superimposed by the adder 6 and then connected to the first input port of the analog quantity switching switch 10. The overrun control opening setting end of the steam regulating valve is connected to the second input port of the analog quantity switching switch 10. The output end of the analog quantity switching switch 10 is connected to the control end of the secondary air preheater steam regulating valve 17.

[0059] The first function generator 1 is used to receive the measured value of the flue gas acid dew point temperature and calculate the expected wall temperature value at the cold end of the air preheater according to the formula "expected wall temperature = flue gas acid dew point temperature + 2°C";

[0060] The third function generator 3 is used to receive the expected wall temperature value at the cold end of the air preheater and the average value of the flue gas temperature at the outlet of the air preheater, and calculate the set value of the air preheater inlet air temperature according to the formula: "wall temperature = 0.5 (flue gas temperature at the outlet of the air preheater + air preheater inlet air temperature) - 5°C";

[0061] The air preheater inlet air temperature controller 4 calculates the deviation between the air preheater inlet air temperature and the set value and outputs a process control command signal for the opening of the secondary air preheater steam regulating valve;

[0062] The measured value of the flue gas acid dew point temperature is successively passed through the differential controller 7, the filtering module 8 and the fifth function generator 9 to obtain a feedforward control signal for the control of the air preheater inlet air temperature;

[0063] When the comprehensive temperature at the cold end is higher than the NH4HSO4 solidification temperature limit value, or when the amount of NH4HSO4 generated in the flue gas is small (SO3 concentration < NH3 concentration; or SO3 concentration > NH3 concentration, and NH3 concentration ≤ 3 ppm), the second AND logic module 14 outputs a signal to select the signal of the first input port of the analog quantity switching switch (i.e., Figure 1 the left input end of the analog quantity switching switch in the figure), and the control system controls the opening of the preheater steam regulating valve according to the superimposed command signal of the output signal of the above-mentioned air preheater inlet air temperature controller and the feedforward control to control the wall temperature of the heat transfer element at the cold end of the air preheater to be higher than the flue gas acid dew point temperature and prevent low-temperature corrosion at the cold end of the air preheater;

[0064] In this implementation method, a logical criterion for the solidification of ammonium bisulfate at the cold end of the air preheater is designed to automatically trigger the overrun action of the air preheater preheater control system. Specifically, the control method includes:

[0065] When the SO3 concentration > NH3 concentration > 3 ppm, the system determines that there is a relatively large amount of NH4HSO4 component in the flue gas. If the comprehensive cold-end temperature is lower than the solidification temperature limit of NH4HSO4 at the same time, the second AND logic module 14 outputs a signal to select the signal of the second input port of the analog switch (i.e., Figure 1 the right input end of the analog switch in

[0066] ). The system automatically triggers an override action to fully open the steam regulating valve of the air preheater quickly, so as to reduce the deposition of ammonium bisulfate in time and relieve the blockage of the air preheater;

[0067] When the system is in the override action, the comprehensive cold-end temperature will rise. When it is higher than the solidification temperature limit of NH4HSO4, or the amount of NH4HSO4 generated in the flue gas is not much (SO3 concentration < NH3 concentration; or SO3 concentration > NH3 concentration, and NH3 concentration ≤ 3 ppm), the system will automatically exit the override control mode. The second AND logic module 14 outputs a signal to select the signal of the first input port of the analog switch (the left input end of the analog switch in the attached drawing). The system adjusts the steam regulating valve of the secondary air heater according to the acid dew point temperature of the flue gas to control the inlet air temperature of the air preheater;

[0068] Since the introduction of derivative control is likely to cause oscillations in the regulating system, making the steam regulating valve of the air preheater act frequently and the actuator structure of the regulating valve is easily damaged, the inlet air temperature controller of the air preheater is designed as a PI controller;

[0069] The output of the first function generator is designed according to "desired wall temperature = acid dew point temperature of flue gas + 2 °C" to calculate the desired wall temperature value;

[0070] The output of the second function generator is designed to be equal to "the average of the data of 3 measuring points of the outlet flue gas temperature of the air preheater" to calculate the average outlet flue gas temperature of the air preheater;

[0071] The third function generator is designed according to "wall temperature = 0.5 (outlet flue gas temperature of air preheater + inlet air temperature of air preheater) - 5 °C" to calculate the inlet air temperature of the air preheater;

[0072] The output of the fourth function generator is designed to be equal to the average of the data of 3 measuring points of the inlet air temperature of the air preheater to calculate the average inlet air temperature of the air preheater;

[0073] The fifth function generator is designed according to a piecewise function;

[0074] The output of the sixth function generator is designed to be equal to the average air temperature at the air preheater inlet + the average flue gas temperature at the air preheater outlet;

[0075] The preset value of the curing temperature limit of ammonium bisulfate is 150°C;

[0076] The preset value of ammonia escape concentration limit is 3ppm;

[0077] The heater steam regulating valve override control opening preset value is 100%;

[0078] The filter time of the filter module is set to 2 seconds.

[0079] According to the above scheme, the automatic control logic of the power station boiler heater based on multi-parameter detection is designed in the DCS configuration software. After the control logic is compiled, it is downloaded to the DCS controller after being checked by the DCS configuration software. The human-machine interface of the air preheater inlet air temperature controller and the preset values ​​of the ammonium bisulfate solidification temperature limit, the preset values ​​of the ammonia escape concentration limit, and the preset values ​​of the heater steam regulating valve override control opening are designed in the screen of the DCS operator station, so that the unit operating personnel can manually correct the controller setting parameters, set the offset, and switch the manual / automatic state on the DCS screen.

[0080] In this implementation, preferably, when the air preheater inlet air temperature is subjected to a disturbance test with a constant value of 10% of the rated temperature, the transition process attenuation rate ψ should be 0.9 to 0.95, and the stabilization time is required to be less than 100s.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A power station boiler air heater automatic control system based on multi-parameter detection, characterized in that: include: An air preheater inlet air temperature controller, a first function generator, a second function generator, a third function generator, a fourth function generator, a fifth function generator, a sixth function generator, an adder, a differential controller, a filter module, a first high value judgment module, a second high value judgment module, a low value judgment module, a first AND gate logic module, a second AND gate logic module and an analog quantity switching switch; The first function generator is used to receive the actual measured value of the flue gas acid dew point temperature and generate the expected wall temperature value of the air preheater cold end, the second function generator is used to receive the actual measured values ​​of the three flue gas temperature measuring points at the air preheater outlet and generate the average value of the flue gas temperature at the air preheater outlet, the third function generator is used to receive the expected wall temperature value of the air preheater cold end and the average value of the flue gas temperature at the air preheater outlet and generate the set value of the air preheater inlet air temperature, the output end of the third function generator is connected to the positive input end of the air preheater inlet air temperature controller, the fourth function generator is used to receive the actual measured values ​​of the three air temperature measuring points at the air preheater inlet and generate the average value of the air preheater inlet air temperature, and the output end of the fourth function generator is connected to the negative input end of the air preheater inlet air temperature controller; The first high value judgment module is used to receive the actual value of ammonia escape concentration and the upper limit value of ammonia escape concentration, and the output end of the first high value judgment module is connected to the first input end of the first AND gate logic module; the second high value judgment module is used to receive the actual value of sulfur trioxide concentration in the flue gas at the denitration outlet and the actual value of ammonia escape concentration, and the output end of the second high value judgment module is connected to the second input end of the first AND gate logic module; The sixth function generator is used to receive the average value of the air preheater inlet air temperature and the average value of the air preheater outlet flue gas temperature and generate the measured value of the cold end comprehensive temperature of the air preheater. The low value judgment module is used to receive the measured value of the cold end comprehensive temperature of the air preheater and the lower limit value of the ammonium bisulfate solidification temperature at the output end of the sixth function generator. The output end of the low value judgment module is connected to the first input end of the second AND gate logic module, the output end of the first AND gate logic module is connected to the second input end of the second AND gate logic module, and the output end of the second AND gate logic module is connected to the switching trigger signal input end of the analog quantity switching switch; The measured value of the flue gas acid dew point temperature is successively input into the adder after passing through the differential controller, the filtering module and the fifth function generator. The output of the air preheater inlet air temperature controller and the output of the fifth function generator are superimposed by the adder and connected to the first input end of the analog quantity switching switch. The override action setting value of the heater steam regulating valve is connected to the second input end of the analog quantity switching switch. The output end of the analog quantity switching switch is connected to the control end of the secondary air heater steam regulating valve.

2. The automatic control system for power station boiler air heater based on multi-parameter detection according to claim 1, characterized in that: The measured value of the flue gas acid dew point temperature passes through the differential controller, the filter module and the fifth function generator in sequence to obtain the feedforward signal for the air preheater inlet air temperature control, so that the control system responds to the change of the flue gas acid dew point temperature and performs dynamic compensation for the air preheater inlet air temperature control.

3. The automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to claim 1 or 2, characterized in that when the amount of NH4HSO4 generated by the flue gas is small, or when the comprehensive cold-end temperature is higher than the solidification temperature limit of NH4HSO4, the analog switch selects to conduct the command signal after the superposition of the output of the air preheater inlet air temperature controller and the feedforward control, and adjusts the steam regulating valve of the secondary air warm air heater according to the acid dew point temperature of the flue gas to control the inlet air temperature of the air preheater; The situation that the amount of NH4HSO4 generated by the flue gas is small includes: SO3 concentration < NH3 concentration; or, SO3 concentration > NH3 concentration and NH3 concentration ≤ 3 ppm.

4. The automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to claim 1 or 2, characterized in that when the amount of NH4HSO4 generated by the flue gas is large and the comprehensive cold-end temperature is lower than the solidification temperature limit of NH4HSO4, the analog switch selects to conduct the override control and fully opens the steam regulating valve of the warm air heater; The situation that the amount of NH4HSO4 generated by the flue gas is large includes: SO3 concentration > NH3 concentration > 3 ppm.

5. The automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to claim 1 or 2, characterized in that when the comprehensive cold-end temperature rises and is higher than the solidification temperature limit of NH4HSO4, or when the amount of NH4HSO4 generated by the flue gas is small, the system automatically exits the override control mode, and adjusts the steam regulating valve of the secondary air warm air heater according to the acid dew point temperature of the flue gas to control the inlet air temperature of the air preheater; The situation that the amount of NH4HSO4 generated by the flue gas is small includes: SO3 concentration < NH3 concentration; or, SO3 concentration > NH3 concentration and NH3 concentration ≤ 3 ppm.

6. The automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to claim 1 or 2, characterized in that The first function generator is used to receive the measured value of the acid dew point temperature of the flue gas, and calculates the expected wall temperature value of the cold end of the air preheater according to the following formula: expected wall temperature = acid dew point temperature of the flue gas + 2°C; The third function generator is used to receive the expected wall temperature value of the cold end of the air preheater and the average value of the outlet flue gas temperature of the air preheater, and calculates the set value of the inlet air temperature of the air preheater according to the following formula: wall temperature = 0.5 (outlet flue gas temperature of the air preheater + inlet air temperature of the air preheater) - 5°C; The air preheater inlet air temperature controller calculates the deviation between the inlet air temperature of the air preheater and the set value and outputs the process control command signal for the opening of the steam regulating valve of the secondary air warm air heater.

7. The automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to claim 1 or 2, characterized in that The output of the second function generator is designed by taking the average of the data of 3 measuring points of the outlet flue gas temperature of the air preheater to calculate the average value of the outlet flue gas temperature of the air preheater; The output of the fourth function generator is designed by taking the average of the data of 3 measuring points of the inlet air temperature of the air preheater to calculate the average value of the inlet air temperature of the air preheater; The fifth function generator is designed according to a piecewise function; The output of the sixth function generator is designed to be equal to the average value of the inlet air temperature of the air preheater + the average value of the outlet flue gas temperature of the air preheater.

8. The automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to claim 1 or 2, characterized in that The preset value of the solidification temperature limit of ammonium bisulfate is 150°C; The preset value of the ammonia slip concentration limit is 3 ppm.

9. The automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to claim 1 or 2, characterized in that The preset value of the override control opening of the warm air heater steam regulating valve is 100%; The filtering time of the filtering module is set to 2 seconds.

10. A method for automatic control of a power station boiler air heater based on multi-parameter detection, characterized in that: Using the automatic control system for the warm air heater of a power plant boiler based on multi-parameter detection according to any one of claims 1-9, includes the following process: When the amount of NH4HSO4 generated by the flue gas is small, or the cold-end comprehensive temperature is higher than the solidification temperature limit of NH4HSO4, the analog switch selects to conduct the command signal after the superposition of the output of the air preheater inlet air temperature controller and the feedforward control, and adjusts the secondary air warm air heater steam regulating valve according to the flue gas acid dew point temperature to control the air preheater inlet air temperature; When the amount of NH4HSO4 generated by the flue gas is large and the cold-end comprehensive temperature is lower than the solidification temperature limit of NH4HSO4, the analog switch selects to conduct the override control and fully opens the warm air heater steam regulating valve; When the cold-end comprehensive temperature rises and is higher than the solidification temperature limit of NH4HSO4, or when the amount of NH4HSO4 generated by the flue gas is small, the system automatically exits the override control mode, and adjusts the secondary air warm air heater steam regulating valve according to the flue gas acid dew point temperature to control the air preheater inlet air temperature; During the process of adjusting the secondary air warm air heater steam regulating valve according to the flue gas acid dew point temperature to control the air preheater inlet air temperature, when the flue gas acid dew point temperature fluctuates, the change amount of the flue gas acid dew point temperature is used as the feedforward signal for the control of the air preheater warm air heater to perform dynamic compensation for the control of the air preheater inlet air temperature; Among them, the amount of NH4HSO4 generated by the flue gas is small, including: SO3 concentration < NH3 concentration; or, SO3 concentration > NH3 concentration and NH3 concentration ≤ 3 ppm; the amount of NH4HSO4 generated by the flue gas is large, including: SO3 concentration > NH3 concentration > 3 ppm.

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