Automatic control system and method for flue gas temperature and water temperature in low-temperature economizer of thermal power unit

Abstract

An automatic control system and method for flue gas temperature and water temperature in a low-temperature economizer of a thermal power unit, the system comprising a low-temperature economizer water volume regulating valve installed at the outlet of No. 7 low-pressure heater and a PID controller connected thereto; a low-pressure inlet water intake regulating valve installed at the inlet of No. 8 low-pressure heater and a PID controller connected thereto; a booster circulation pump installed at the end of the low-temperature economizer system and a PID controller connected thereto, the flue gas temperature in the low-temperature economizer is controlled by the low-temperature economizer water volume regulating valve; the booster circulation pump and the low-pressure inlet water intake regulating valve jointly control the water temperature in the low-temperature economizer, when the booster circulation pump and the low-pressure inlet water intake regulating valve are put into automatic operation at the same time, the system will automatically determine which regulating loop is in effect according to the current operating status, and the two will not affect each other, saving a lot of work for the operators, and also providing further guarantee for the economical and safe operation of the power plant.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control of thermal power plants, and in particular to an automatic control system and method for flue gas temperature and water temperature in a low-temperature economizer of a thermal power unit. Background Art

[0002] In recent years, the installed capacity of thermal power plants in my country has continued to grow rapidly, and the installed capacity in service and under construction has ranked among the top in the world. At present, thermal power plants consume 50% of my country's total coal production, and their flue gas heat loss is the largest item among the various heat losses of the boiler, generally 5% to 8%, accounting for about 80% or more of the total heat loss of the boiler. The main factor affecting the heat loss of flue gas is the boiler flue gas temperature. Under normal circumstances, the flue gas heat loss increases by 0.6% to 1.0% for every 10°C increase in the flue gas temperature. The flue gas temperature of boilers in my country's active thermal power units is generally maintained at around 125 to 150°C, and high flue gas temperature is a common phenomenon. In addition, the increase in flue gas temperature increases the flue gas volume, which affects the working environment of the induced draft fan, dust collector, and desulfurization equipment. Therefore, reasonably reducing the boiler flue gas temperature plays a vital role in improving the safety and economy of the unit. At the same time, with the increase in flue gas loss, the corresponding coal consumption will also increase. Therefore, reducing the flue gas temperature is of great practical significance for saving fuel and reducing pollution.

[0003] In practice, there are many boiler technology transformations aimed at reducing the exhaust gas temperature. However, many solutions are difficult to implement due to the small space of the tail flue of most power plants, high requirements for anti-wear and anti-corrosion, and small pressure head margin of the induced draft fan. At present, most of the thermal power units in my country have adopted the solution of installing low-temperature economizer devices on the flue to reduce the exhaust gas temperature, reduce exhaust losses, and improve the economic efficiency of power plant operation.

[0004] The specific plan is: the low-temperature economizer is arranged in the horizontal flue at the entrance of the electrostatic precipitator, and each unit is equipped with 4 low-temperature economizers, using H-shaped finned tubes, double tube rings, sequential and countercurrent arrangements. The working principle is that the condensate absorbs the exhaust heat in the low-temperature economizer, reduces the exhaust temperature, and the condensate itself is heated. The condensate with increased temperature returns to the low-pressure heater system to improve the overall thermal efficiency of the unit.

[0005] After the boiler low-temperature economizer was modified, the units all reduced the boiler exhaust temperature and reduced exhaust losses. According to the principle of thermodynamics, the condensate of the turbine absorbs the heat of the flue gas at the tail of the boiler, increases the temperature of the condensate of the turbine, and then increases the boiler feed water temperature, and the overall coal consumption of the unit will be reduced. Using the waste heat of the flue gas of the boiler to heat the condensate, the condensate temperature is increased, which is equivalent to adding excess heat to the steam extraction system of the steam turbine, increasing the effective steam volume entering the steam turbine, and increasing the equivalent enthalpy drop of the unit. It can be seen that after the installation of the low-temperature economizer, the heat consumption rate of the steam turbine is reduced. Taking the condenser as the main body of analysis, after the installation of the low-temperature economizer, the condensate temperature is higher than before the installation, the steam extraction volume of the low-pressure heater of the steam turbine will be reduced, and the excess exhaust flow of the low-pressure cylinder will increase, thereby reducing the condenser vacuum.

[0006] The stability of low-temperature economizer operating parameters is closely related to changes in external loads and changes in internal factors of low-temperature economizers. As long as any of the above factors change, the stability and safety of low-temperature economizer operation will be affected. Therefore, a series of controls and adjustments must be made to the low-temperature economizer to make the parameters of the low-temperature economizer adapt to external changes or changes in internal factors, so as to achieve safe and economical operation. At present, after most of the thermal power units in my country have been transformed by low-temperature economizers, the control systems are running in manual mode and cannot be put into automatic operation. The reason for this phenomenon is the lack of control strategies that meet the requirements. It brings a great burden to the operation of the operating personnel and increases the danger and uncertainty of the entire system. Therefore, it is urgent to take measures to optimize and transform the relevant control systems of thermal power units after the low-temperature economizer transformation. Summary of the invention

[0007] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide an automatic control system and method for the flue gas temperature and water temperature in the low-temperature economizer of a thermal power unit, which can meet the needs of automatic operation of the flue gas temperature and water temperature control circuits of the thermal power unit after the low-temperature economizer is modified, thereby providing further guarantee for the economic and safe operation of the power plant.

[0008] The present invention is implemented by the following technical solutions:

[0009] An automatic control system for flue gas temperature and water temperature in a low-temperature economizer of a thermal power unit, comprising a condensate 1, a condensate pump 2 of a condensate pressurizing device, a shaft seal heater 3 of a condensate heating device, a No. 8 low-pressure heater 4 and a No. 7 low-pressure heater 5 of the condensate heating device, a low-temperature economizer water flow regulating valve 6 installed at the outlet of the No. 7 low-pressure heater 5 and a first PID controller 14 connected thereto, a No. 6 low-pressure heater 26 of the condensate heating device of a deaerator, a low-pressure inlet water intake regulating valve 7 installed at the inlet of the No. 8 low-pressure heater 4 and a second PID controller 14 connected thereto. ID controller 15, a booster circulation pump 13 installed at the end of the low-temperature economizer system and a third PID controller 16 connected thereto, a low-temperature economizer A outlet flue gas temperature measuring point 8 installed at the outlet of the low-temperature economizer A, a low-temperature economizer B outlet flue gas temperature measuring point 9 installed at the outlet of the low-temperature economizer B, a low-temperature economizer C outlet flue gas temperature measuring point 10 installed at the outlet of the low-temperature economizer C, a low-temperature economizer D outlet flue gas temperature measuring point 11 installed at the outlet of the low-temperature economizer D, and a low-temperature economizer inlet water temperature measuring point 12 installed at the outlet of the low-temperature addition inlet water intake regulating valve 7.

[0010] The input signal of the first PID controller 14 includes three paths. The first path is the outlet flue gas temperature that needs to be controlled and adjusted. The control object selects the minimum value of the outlet flue gas temperature through the small selection controller 17; the second path is the control set value of the outlet flue gas temperature, which is realized by the low-temperature economizer outlet flue gas temperature set value 22. The implementation method of this set value is manual setting by the operator. The outlet flue gas temperature passes through the large selection controller 18 to select the maximum value of the flue gas temperature. The maximum value of the flue gas temperature output by the large selection controller 18 will be superimposed on the low-temperature economizer outlet flue gas temperature set value 22 through the adder 19 to form the final input signal entering the PID controller 14; the third path is the differential loop of the unit load instruction 21, which is realized by the first differential controller 20 and finally enters the feedforward part of the first PID controller 14; the first PID controller 14 includes proportional P and integral I control functions.

[0011] The input signal of the second PID controller 15 includes three paths. The first path is the low-temperature economizer inlet water temperature measuring point 12, which is the control object of the second PID controller; the second path is the low-temperature economizer inlet water temperature setting value 23, which is implemented by manual setting by the operator; the third path is the differential loop of the unit load instruction 21, which is implemented by the differential controller 24 and finally enters the feedforward part of the PID controller 15. The PID controller 15 includes proportional P and integral I control functions.

[0012] The input signal of the third PID controller 16 includes three paths. The first path is the low-temperature economizer inlet water temperature measuring point 12, which is the control object of the controller; the second path is the low-temperature economizer inlet water temperature setting value 23, which is implemented by manual setting by the operator; the third path is the differential loop of the unit load instruction 21, which is implemented by the second differential controller 25 and finally enters the feedforward part of the PID controller 16. The PID controller 16 includes proportional P and integral I control functions.

[0013] The low-temperature economizer A outlet flue gas temperature measuring point 8), the low-temperature economizer B outlet flue gas temperature measuring point 9, the low-temperature economizer C outlet flue gas temperature measuring point 10 and the low-temperature economizer D outlet flue gas temperature measuring point 11 are each arranged with three measuring points, and the low-temperature economizer inlet water temperature measuring point 12 is arranged with two measuring points.

[0014] The working method of the automatic control system of flue gas temperature and water temperature in the low-temperature economizer of the thermal power unit is that when the unit is operating normally, the main water supply circuit passes through the condensate 1 from the hot well, which is pressurized and heated by the condensate pump 2 and the shaft seal heater 3 in turn, and then continues to be heated by the No. 8 low-pressure heater 4 and the No. 7 low-pressure heater 5. The heated condensate enters the low-temperature economizer water flow regulating valve 6 for regulation, and finally enters the deaerator after being heated by the No. 6 low-pressure heater 26; enters the low-temperature economizer system to cool the flue gas temperature Water is taken from the inlet of No. 8 low-pressure heater 4, and its temperature is lower than the flue gas temperature and the outlet water temperature in the low-temperature economizer; the outlet of No. 7 low-pressure heater 5 has a temperature higher than the inlet of No. 8 low-pressure heater 4, and the unit's demand for flue gas temperature is met through the joint regulation of the low-temperature economizer water volume regulating valve 6, the low-pressure inlet water intake regulating valve 7 and the boost circulation pump 13; the water after cooling the flue gas temperature is circulated through the low-temperature economizer system, and then merged into the main feed water system before the No. 6 low-pressure heater 26, and then enters the deaerator.

[0015] The common adjustment method of the low-temperature economizer water flow regulating valve 6, the low-temperature addition inlet water intake regulating valve 7 and the booster circulation pump 13 is as follows: wherein, the low-temperature economizer water flow regulating valve 6 adjusts the low-temperature economizer outlet flue gas temperature, and the low-temperature addition inlet water intake regulating valve 7 and the booster circulation pump 13 jointly adjust the economizer inlet water temperature;

[0016] The outlet flue gas temperature of each low-temperature economizer is controlled by a low-temperature economizer water flow regulating valve 6. Multiple flue gas measuring points are arranged at the outlets of the four low-temperature economizers, and the median processing is performed on the multiple measuring points. Considering that the long-term low-temperature operation of the flue gas will cause low-temperature corrosion to the pipe wall, the four outlet flue gas temperature measuring points that have been screened are passed through a small selection controller 17 to obtain the minimum flue gas temperature value as the controlled object of the first PID controller 14. The control setting value of the outlet flue gas temperature is the low-temperature economizer outlet flue gas temperature setting value 22, and the setting value is realized by manual setting by the operator. The first PID controller 14 includes proportional P action and integral I action. When the low-temperature economizer outlet flue gas temperature is When the minimum temperature value increases, a positive deviation occurs between the actual minimum value of the low-temperature economizer flue gas temperature and the low-temperature economizer outlet flue gas temperature set value 22 signal, so that the proportional P action and the integral I action of the PID controller 14 start to act, and an instruction to close the low-temperature economizer water volume regulating valve 6 is issued, thereby lowering the flue gas temperature by lowering the water temperature; similarly, when the minimum value of the low-temperature economizer outlet flue gas temperature decreases, a negative deviation occurs between the actual minimum value of the low-temperature economizer flue gas temperature and the low-temperature economizer outlet flue gas temperature set value 22 signal, so that the proportional P action and the integral I action of the PID controller 14 start to act, and an instruction to open the low-temperature economizer water volume regulating valve 6 is issued, thereby raising the flue gas temperature by raising the water temperature;

[0017] In order to prevent the maximum value of the outlet flue gas temperature from being too high, the four outlet flue gas temperature measuring points that have been screened out are passed through the general controller 18 to obtain the maximum flue gas temperature value. Under abnormal working conditions, when the maximum flue gas temperature value of the low-temperature economizer is greater than the low-temperature economizer outlet flue gas temperature setting value of 223℃--6℃, the low-temperature economizer outlet flue gas temperature setting value 22 is slightly corrected downward through the adder 19 to form the final low-temperature economizer outlet flue gas temperature control setting value to enter the regulation;

[0018] Considering the changing working condition of the unit load instruction 21, the differential controller 20 will be used to advance the low-temperature economizer water flow regulating valve 6 instruction; when the unit load instruction 21 increases, the flue gas volume and flue gas temperature will increase. At this time, the differential controller 20 will directly give an instruction to close the low-temperature economizer water flow regulating valve 6 to maintain the temperature stability; when the unit load instruction 21 decreases, the flue gas volume and flue gas temperature will decrease. At this time, the differential controller 20 will directly give an instruction to open the low-temperature economizer water flow regulating valve 6 to maintain the temperature stability;

[0019] Finally, considering that the low-temperature economizer water flow regulating valve 6 is the main regulating valve for the deaerator, it is necessary to ensure that the entire unit has sufficient feed water flow, and the minimum flow protection link is designed. When the actual feed water flow is lower than the preset feed water flow value, the low-temperature economizer water flow regulating valve 6 is prohibited from continuing to close;

[0020] The booster circulation pump 13 and the low-temperature inlet water intake regulating valve 7 are used to jointly adjust the low-temperature economizer inlet water temperature. The low-temperature economizer inlet water temperature measuring point 12 is arranged with multiple measuring points, and the average value of the multiple measuring points is processed; when the unit is running in the low-load section, the inlet water temperature is low. At this time, the booster circulation pump 13 is used for adjustment. The third PID controller 16 is used for adjustment, including proportional P action and integral I action. When the low-temperature economizer inlet water temperature measuring point 12 increases, a positive deviation occurs between the actual inlet water temperature of the low-temperature economizer and the low-temperature economizer inlet water temperature set value 23 signal, so that the proportional P action and integral I action of the PID controller 16 start to act, and an instruction to turn off the booster circulation pump 13 is issued to meet the water temperature demand; similarly, when the low-temperature economizer inlet water temperature measuring point 12 decreases, a negative deviation occurs between the actual inlet water temperature of the low-temperature economizer and the low-temperature economizer inlet water temperature set value 23 signal, so that the proportional P action and integral I action of the PID controller 16 start to act, and an instruction to turn on the booster circulation pump 13 is issued to meet the water temperature demand;

[0021] At the same time, when the unit load instruction 21 changes, the differential controller 25 will also be used to advance the instruction of the boost circulation pump 13 to meet the temperature requirement; when the unit load instruction 21 increases, the flue gas volume and flue gas temperature will increase, and the differential controller 25 will directly give an instruction to turn off the boost circulation pump 13 to meet the temperature requirement; when the unit load instruction 21 decreases, the flue gas volume and flue gas temperature will decrease, and the differential controller 25 will directly give an instruction to turn on the boost circulation pump 13 to meet the temperature requirement;

[0022] When the unit is operating from a low load to a high load section, as the water temperature rises, the booster circulation pump 13 will gradually shut down. When it is closed to 5% opening, if the low-temperature economizer inlet water temperature measuring point 12 is still higher than the low-temperature economizer inlet water temperature setting value 23, it indicates that the booster circulation pump 13 has no adjustment margin, and the system automatically switches to the low-pressure inlet water intake regulating valve 7 to continue to adjust the low-temperature economizer inlet water temperature measuring point 12; the adjustment is adjusted by the second PID controller 15, including proportional P action and integral I action;

[0023] When the low-temperature economizer inlet water temperature measuring point 12 increases, a positive deviation occurs between the actual low-temperature economizer inlet water temperature and the low-temperature economizer inlet water temperature set value 23 signal, so that the proportional P function and the integral I function of the PID controller 15 start to act, and issue an instruction to open the low-temperature addition inlet water intake regulating valve 7 to meet the water temperature demand; similarly, when the low-temperature economizer inlet water temperature measuring point 12 decreases, a negative deviation occurs between the actual low-temperature economizer inlet water temperature and the low-temperature economizer inlet water temperature set value 23 signal, so that the proportional P function and the integral I function of the PID controller 15 start to act, and issue an instruction to close the low-temperature addition inlet water intake regulating valve 7 to meet the water temperature demand;

[0024] At the same time, when the unit load instruction 21 changes, the differential controller 24 will also act in advance to initiate the low-pressure addition inlet water intake regulating valve 7 instruction to meet the temperature requirement; when the unit load instruction 21 increases, the flue gas volume and flue gas temperature will increase, and the differential controller 24 will directly issue an instruction to open the low-pressure addition inlet water intake regulating valve 7 to meet the temperature requirement; when the unit load instruction 21 decreases, the flue gas volume and flue gas temperature will decrease, and the differential controller 24 will directly issue an instruction to close the low-pressure addition inlet water intake regulating valve 7 to meet the temperature requirement;

[0025] When the unit switches from high load to low load operation, the low-pressure inlet water intake regulating valve 7 is gradually closed. When it is closed to the lower limit, if the low-temperature economizer inlet water temperature measuring point 12 is still lower than the low-temperature economizer inlet water temperature setting value 23, it indicates that the low-pressure inlet water intake regulating valve 7 has no adjustment margin, and the system automatically switches to the boost circulation pump 13 to continue to adjust the low-temperature economizer inlet water temperature measuring point 12.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) In the low-temperature economizer operating circuit, the control object of each automatic control valve should be clearly defined, and the working range of each automatic control valve should be reasonably arranged.

[0028] (2) For the control of the low-temperature economizer inlet water temperature, the idea of ​​jointly controlling the booster circulation pump and the low-pressure inlet water intake regulating valve is proposed, and the two sets of automatic control logics switch autonomously and without interference with each other according to the operating load conditions. When both are put into automatic operation at the same time, the system will automatically determine which regulation loop is effective according to the current operating status, and the two will not affect each other.

[0029] (3) Considering variable load conditions, intelligently predict the change in steam temperature when the load changes, and intervene in advance.

[0030] (4) The control method of the present invention can meet the requirements of automatic operation of the flue gas temperature and water temperature control loops of thermal power units after the low-temperature economizer is modified. This can greatly reduce the operating burden of operators and provide further guarantee for the economic and safe operation of power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the control system of the present invention.

[0032] Description of reference numerals:

[0033] 1——condensate; 2——condensate pump; 3——shaft seal heater;

[0034] 4-8 low-pressure heaters; 5-7 low-pressure heaters;

[0035] 6——Low-temperature economizer water flow regulating valve; 7——Low-temperature inlet water intake regulating valve;

[0036] 8——Measuring point of flue gas temperature at the outlet of low-temperature economizer A;

[0037] 9——Measuring point of flue gas temperature at the outlet of low-temperature economizer B;

[0038] 10——Measuring point of flue gas temperature at the outlet of low-temperature economizer C;

[0039] 11——Measuring point of flue gas temperature at outlet of low-temperature economizer D;

[0040] 12——Measuring point of water temperature at the inlet of low-temperature economizer;

[0041] 13——boost circulation pump; 14——first PID controller; 15——second PID controller; 16——third PID controller;

[0042] 17——small selection controller; 18——large selection controller; 19——adder; 20——first differential controller;

[0043] 21——Unit load instruction; 22——Low-temperature economizer outlet flue gas temperature setting value;

[0044] 23——Low-temperature economizer inlet water temperature setting value; 24——Differential controller; 25——Second differential controller;

[0045] 26--No. 6 low-pressure heater. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0047] like Figure 1As shown, the present invention is an automatic control system for flue gas temperature and water temperature in a low-temperature economizer of a thermal power unit, comprising condensate 1 from a hot well, a condensate pump 2 of a condensate pressurizing device, a shaft seal heater 3 of a condensate heating device, a No. 8 low-pressure heater 4 and a No. 7 low-pressure heater 5 of the condensate heating device, a low-temperature economizer water flow regulating valve 6 installed at the outlet of the No. 7 low-pressure heater 5 and a first PID controller 14 connected thereto, a No. 6 low-pressure heater 26 of the condensate heating device to the deaerator, a low-pressure inlet water intake regulating valve 7 installed at the inlet of the No. 8 low-pressure heater 4 and a second PID controller 15 connected thereto, and a low-temperature economizer system end. The boost circulation pump 13 and the third PID controller 16 connected thereto, the low-temperature economizer A outlet flue gas temperature measuring point 8 installed at the outlet of the low-temperature economizer A, usually three measuring points are arranged, the low-temperature economizer B outlet flue gas temperature measuring point 9 installed at the outlet of the low-temperature economizer B, usually three measuring points are arranged, the low-temperature economizer C outlet flue gas temperature measuring point 10 installed at the outlet of the low-temperature economizer C, usually three measuring points are arranged, the low-temperature economizer D outlet flue gas temperature measuring point 11 installed at the outlet of the low-temperature economizer D, usually three measuring points are arranged, the low-temperature economizer inlet water temperature measuring point 12 installed at the outlet of the low-temperature addition inlet water intake regulating valve 7, usually two measuring points are arranged. The input signal of the first PID controller 14 includes three paths. The first path is the outlet flue gas temperature that needs to be controlled and adjusted. The control object selects the minimum value of the outlet flue gas temperature through the small selection controller 17. The function of the small selection controller 17 is to select the minimum value of the input signal as the output signal. The significance of controlling the minimum value is to prevent the occurrence of low-temperature corrosion in the low-temperature economizer; the second path is the control set value of the outlet flue gas temperature, which is realized by the low-temperature economizer outlet flue gas temperature set value 22. The implementation method of this set value is manual setting by the operator. The outlet flue gas temperature passes through the large selection controller 18 to select the maximum value of the flue gas temperature. The function of 18 is to select the maximum value of the input signal as the output signal. The maximum value of the output flue gas temperature will be superimposed on the low-temperature economizer outlet flue gas temperature set value 22 through the adder 19. The purpose of this part is to prevent the controlled flue gas temperature from being too high, forming the input signal that finally enters the PID controller 14; the third path is the differential loop of the unit load instruction 21, which is implemented by the first differential controller 20 and finally enters the feedforward part of the first PID controller 14. As a part of the first PID controller 14, the feedforward can make the output more accurate and faster. The first PID controller 14 includes proportional P and integral I control functions.The input signal of the second PID controller 15 includes three paths. The first path is the low-temperature economizer inlet water temperature measuring point 12, which is the control object of the controller; the second path is the low-temperature economizer inlet water temperature setting value 23, which is manually set by the operator; the third path is the differential loop of the unit load instruction 21, which is implemented by the differential controller 24, and finally enters the feedforward part of the PID controller 15. The PID controller 15 includes proportional P and integral I control functions. The input signal of the third PID controller 16 includes three paths. The first path is the low-temperature economizer inlet water temperature measuring point 12, which is the control object of the controller; the second path is the low-temperature economizer inlet water temperature setting value 23, which is manually set by the operator; the third path is the differential loop of the unit load instruction 21, which is implemented by the second differential controller 25, and finally enters the feedforward part of the PID controller 16. The PID controller 16 includes proportional P and integral I control functions.

[0048] The specific control method and working principle are as follows: when the unit is operating normally, the main feed water circuit passes through the condensate 1 from the hot well, and is pressurized and heated by the condensate pump 2 and the shaft seal heater 3 in turn, and then continues to heat it through the No. 8 low-pressure heater 4 and the No. 7 low-pressure heater 5. The heated condensate enters the low-temperature economizer water flow regulating valve 6 for regulation, and finally enters the deaerator after being heated by the No. 6 low-pressure heater 26. The water entering the low-temperature economizer system to cool the flue gas temperature is taken from the inlet of the No. 8 low-pressure heater 4, and its temperature is relatively low relative to the flue gas temperature and the outlet water temperature in the low-temperature economizer; the outlet of the No. 7 low-pressure heater 5, its temperature is relatively high relative to the inlet temperature of the No. 8 low-pressure heater 4, and is jointly regulated by the low-temperature economizer water flow regulating valve 6, the low-pressure inlet water intake regulating valve 7 and the boost circulation pump 13 to meet the unit's flue gas temperature requirements. After the water that cools the flue gas temperature circulates through the low-temperature economizer system, it is returned to the main feed water system before the No. 6 low-pressure heater 26, and then enters the deaerator.

[0049] At present, the main reason why the automatic control in the low-temperature economizer system cannot be put into use is that the various regulating gates cannot be effectively coordinated and adjusted, so the present invention aims to propose a practical and effective control strategy. The common adjustment method of the low-temperature economizer water volume regulating valve 6, the low-pressure inlet water intake regulating valve 7 and the booster circulation pump 13 is: wherein, the low-temperature economizer water volume regulating valve 6 adjusts the low-temperature economizer outlet flue gas temperature, and the low-pressure inlet water intake regulating valve 7 and the booster circulation pump 13 jointly adjust the economizer inlet water temperature.

[0050] The design uses the low-temperature economizer water flow regulating valve 6 to control the outlet flue gas temperature of each low-temperature economizer. The design first processes the outlet flue gas temperature of the controlled quantity. The outlets of the four low-temperature economizers are all arranged with flue gas measuring points. Among them, the outlet flue gas temperature measuring point 8 of the low-temperature economizer A is usually arranged with three measuring points, and the three measuring points are processed by taking the median of three; the outlet flue gas temperature measuring point 9 of the low-temperature economizer B is usually arranged with three measuring points, and the three measuring points are processed by taking the median of three; the outlet flue gas temperature measuring point 10 of the low-temperature economizer C is usually arranged with three measuring points, and the three measuring points are processed by taking the median of three; the outlet flue gas temperature measuring point 11 of the low-temperature economizer D is usually arranged with three measuring points, and the three measuring points are processed by taking the median of three. Taking into account the problem that long-term low-temperature operation of flue gas will cause low-temperature corrosion to the pipe wall, the four outlet flue gas temperature measurement points that have been screened out are passed through the small selection controller 17 to obtain the minimum flue gas temperature value as the controlled object of the first PID controller 14, and the control setting value of the outlet flue gas temperature is the low-temperature economizer outlet flue gas temperature setting value 22, which is implemented by manual setting by the operator; the first PID controller 14 adjustment includes proportional P action and integral I action. When the minimum value of the low-temperature economizer outlet flue gas temperature increases, a positive deviation occurs between the actual minimum value of the low-temperature economizer flue gas temperature and the low-temperature economizer outlet flue gas temperature setting value 22 signal, so that the proportional P action and integral I action of the PID controller 14 start to act, and an instruction to close the low-temperature economizer water volume regulating valve 6 is issued, thereby lowering the flue gas temperature by lowering the water temperature. Similarly, when the minimum value of the low-temperature economizer outlet flue gas temperature decreases, a negative deviation appears between the actual minimum value of the low-temperature economizer flue gas temperature and the low-temperature economizer outlet flue gas temperature set value 22 signal, causing the proportional P action and integral I action of the PID controller 14 to start to act, issuing an instruction to open the low-temperature economizer water flow regulating valve 6, thereby increasing the flue gas temperature by increasing the water temperature.

[0051] In addition, considering the uneven flow of flue gas inside the boiler, it may cause a large deviation in the outlet flue gas temperature of each low-temperature economizer. In order to prevent the maximum value of the outlet flue gas temperature from being too high, the four selected outlet flue gas temperature measurement points are passed through the large selection controller 18 to obtain the maximum flue gas temperature value. Under abnormal operating conditions, when the maximum flue gas temperature value of the low-temperature economizer is greater than the low-temperature economizer outlet flue gas temperature setting value of about 225°C, the low-temperature economizer outlet flue gas temperature setting value 22 is slightly corrected downward by the adder 19 to form the final low-temperature economizer outlet flue gas temperature setting value for regulation.

[0052] Considering the changing working condition of the unit load instruction 21, the differential controller 20 will be used to advance the low-temperature economizer water flow regulating valve 6 instruction. When the unit load instruction 21 increases, the flue gas volume and flue gas temperature will increase. At this time, the differential controller 20 will directly give an instruction to close the low-temperature economizer water flow regulating valve 6 to maintain temperature stability; when the unit load instruction 21 decreases, the flue gas volume and flue gas temperature will decrease. At this time, the differential controller 20 will directly give an instruction to open the low-temperature economizer water flow regulating valve 6 to maintain temperature stability.

[0053] Finally, considering that the low-temperature economizer water flow regulating valve 6 is the main regulating valve for the deaerator, it is necessary to ensure that the entire unit has sufficient feed water flow. A special minimum flow protection link is designed. When the actual feed water flow is lower than the preset feed water flow value, the regulating valve is prohibited from continuing to close. Taking a 660MW ultra-supercritical unit as an example, according to different loads, the required feed water flow is preset as follows:

[0054] Load MW 0 300 420 600 650 660 700 Flow rate t / h 500 650 900 1300 1400 1450 1500

[0055] Other units of different capacities can set such functions according to the instructions provided by the boiler manufacturer.

[0056] The design uses the booster circulation pump 13 and the low-temperature inlet water intake regulating valve 7 to jointly adjust the low-temperature economizer inlet water temperature. The low-temperature economizer inlet water temperature measuring point 12 is usually arranged with two measuring points, and the two average values ​​are processed. When the unit is running in the low load section, the inlet water temperature is low. At this time, it is adjusted by the boost circulation pump 13. The adjustment is made by the third PID controller 16, including proportional P action and integral I action. When the low-temperature economizer inlet water temperature measuring point 12 increases, a positive deviation appears between the actual inlet water temperature of the low-temperature economizer and the low-temperature economizer inlet water temperature setting value 23 signal, so that the proportional P action and integral I action of the PID controller 16 start to act, and an instruction to turn off the boost circulation pump 13 is issued to meet the water temperature requirement; similarly, when the low-temperature economizer inlet water temperature measuring point 12 decreases, a negative deviation appears between the actual inlet water temperature of the low-temperature economizer and the low-temperature economizer inlet water temperature setting value 23 signal, so that the proportional P action and integral I action of the PID controller 16 start to act, and an instruction to turn on the boost circulation pump 13 is issued to meet the water temperature requirement.

[0057] At the same time, when the unit load instruction 21 changes, the differential controller 25 will also be used to advance the instruction of the boost circulation pump 13 to meet the temperature requirement. When the unit load instruction 21 increases, the flue gas volume and flue gas temperature will increase. At this time, the differential controller 25 will directly give an instruction to turn off the boost circulation pump 13 to meet the temperature requirement; when the unit load instruction 21 decreases, the flue gas volume and flue gas temperature will decrease. At this time, the differential controller 25 will directly give an instruction to turn on the boost circulation pump 13 to meet the temperature requirement.

[0058] When the unit is running from low load to high load, as the water temperature rises, the booster circulation pump 13 will gradually close. When it is closed to 5% opening, if the low-temperature economizer inlet water temperature measuring point 12 is still higher than the low-temperature economizer inlet water temperature setting value 23, it means that the booster circulation pump 13 has no adjustment margin, and the system automatically switches to the low-pressure inlet water intake regulating valve 7 to continue to adjust the low-temperature economizer inlet water temperature measuring point 12. The second PID controller 15 is used for adjustment, including proportional P action and integral I action.

[0059] When the low-temperature economizer inlet water temperature measuring point 12 increases, a positive deviation occurs between the actual low-temperature economizer inlet water temperature and the low-temperature economizer inlet water temperature set value 23 signal, causing the proportional P function and the integral I function of the PID controller 15 to start to act, and issuing an instruction to open the low-temperature addition inlet water intake regulating valve 7 to meet the water temperature requirement; similarly, when the low-temperature economizer inlet water temperature measuring point 12 decreases, a negative deviation occurs between the actual low-temperature economizer inlet water temperature and the low-temperature economizer inlet water temperature set value 23 signal, causing the proportional P function and the integral I function of the PID controller 15 to start to act, and issuing an instruction to close the low-temperature addition inlet water intake regulating valve 7 to meet the water temperature requirement.

[0060] At the same time, when the unit load instruction 21 changes, the differential controller 24 will also be used to advance the low-pressure inlet water intake regulating valve 7 instruction to meet the temperature requirement. When the unit load instruction 21 increases, the flue gas volume and flue gas temperature will increase. At this time, the differential controller 24 will directly give an instruction to open the low-pressure inlet water intake regulating valve 7 to meet the temperature requirement; when the unit load instruction 21 decreases, the flue gas volume and flue gas temperature will decrease. At this time, the differential controller 24 will directly give an instruction to close the low-pressure inlet water intake regulating valve 7 to meet the temperature requirement.

[0061] When the unit switches from high load to low load operation, the low-pressure inlet water intake regulating valve 7 is gradually closed. When it is closed to the lower limit, if the low-temperature economizer inlet water temperature measuring point 12 is still lower than the low-temperature economizer inlet water temperature setting value 23, it indicates that the low-pressure inlet water intake regulating valve 7 has no adjustment margin, and the system automatically switches to the boost circulation pump 13 to continue to adjust the low-temperature economizer inlet water temperature measuring point 12.

Claims

1. An automatic control system for flue gas temperature and water temperature in a low-temperature economizer of a thermal power unit, characterized in that: It includes condensate connected in sequence, a condensate pump of a condensate pressurizing device, a shaft seal heater of a condensate heating device, a No. 8 low-pressure heater and a No. 7 low-pressure heater of the condensate heating device, a low-temperature economizer water volume regulating valve installed at the outlet of the No. 7 low-pressure heater and a first PID controller connected thereto, a No. 6 low-pressure heater of the condensate heating device to the deaerator, a low-pressure inlet water intake regulating valve installed at the inlet of the No. 8 low-pressure heater and a second PID controller connected thereto, a booster circulation pump installed at the end of the low-temperature economizer system and a third PID controller connected thereto, a low-temperature economizer A outlet flue gas temperature measuring point installed at the outlet of the low-temperature economizer A, a low-temperature economizer B outlet flue gas temperature measuring point installed at the outlet of the low-temperature economizer B, a low-temperature economizer C outlet flue gas temperature measuring point installed at the outlet of the low-temperature economizer C, a low-temperature economizer D outlet flue gas temperature measuring point installed at the outlet of the low-temperature economizer D, and a low-temperature economizer inlet water temperature measuring point installed at the outlet of the low-temperature economizer inlet water intake regulating valve; The input signal of the first PID controller includes three paths, the first path is the outlet smoke temperature that needs to be controlled and adjusted, and the minimum value of the outlet smoke temperature is selected through the small selection controller; The second route is the control set value of the outlet flue gas temperature, which is realized by the outlet flue gas temperature set value of the low-temperature economizer. The set value is realized by manual setting by the operator. The outlet flue gas temperature passes through the large-scale controller to select the maximum value of the flue gas temperature. The maximum value of the flue gas temperature output by the large-scale controller will be superimposed on the outlet flue gas temperature set value of the low-temperature economizer through the adder to form the input signal that finally enters the first PID controller; the third route is the differential loop of the unit load instruction, which is realized by the first differential controller and finally enters the feedforward part of the first PID controller; the first PID controller includes proportional and integral control functions; The input signal of the second PID controller includes three paths, the first path is the low-temperature economizer inlet water temperature measurement point, which is the control object of the second PID controller; The second path is the low-temperature economizer inlet water temperature set value, which is manually set by the operator; the third path is the differential loop of the unit load command, which is implemented through the differential controller and finally enters the feedforward part of the second PID controller. The second PID controller includes proportional and integral control functions; The input signal of the third PID controller includes three paths, the first path is the low-temperature economizer inlet water temperature measurement point, which is the control object of the controller; The second path is the low-temperature economizer inlet water temperature set value, which is implemented by manual setting by the operator; the third path is the differential loop of the unit load instruction, which is implemented through the second differential controller and finally enters the feedforward part of the third PID controller. The third PID controller includes proportional and integral control functions.

2. The automatic control system for flue gas temperature and water temperature in a low-temperature economizer of a thermal power unit according to claim 1, characterized in that: The low-temperature economizer A outlet flue gas temperature measuring point, the low-temperature economizer B outlet flue gas temperature measuring point, the low-temperature economizer C outlet flue gas temperature measuring point and the low-temperature economizer D outlet flue gas temperature measuring point are each arranged with three measuring points, and the low-temperature economizer inlet water temperature measuring point is arranged with two measuring points.

3. The working method of the automatic control system of flue gas temperature and water temperature in the low temperature economizer of a thermal power plant according to claim 1 or 2, characterized in that: When the unit is operating normally, the main feed water circuit passes through the condensate from the hot well, which is pressurized and heated by the condensate pump and the shaft seal heater in turn, and then continues to be heated by the No. 8 low-pressure heater and the No. 7 low-pressure heater. The heated condensate enters the low-temperature economizer water flow regulating valve for regulation, and finally enters the deaerator after being heated by the No. 6 low-pressure heater; the water entering the low-temperature economizer system to cool the flue gas temperature is taken from the inlet of the No. 8 low-pressure heater, and its temperature is lower than the flue gas temperature and the outlet water temperature in the low-temperature economizer; the outlet of the No. 7 low-pressure heater has a higher temperature than the inlet of the No. 8 low-pressure heater, and is jointly regulated by the low-temperature economizer water flow regulating valve, the low-pressure inlet water intake regulating valve and the booster circulation pump to meet the unit's flue gas temperature requirements; the water after cooling the flue gas temperature circulates through the low-temperature economizer system, and then flows back to the main feed water system before the No. 6 low-pressure heater, and then enters the deaerator.

4. The working method according to claim 3, characterized in that: The common adjustment method of the low-temperature economizer water flow regulating valve, the low-pressure inlet water intake regulating valve and the booster circulation pump is as follows: wherein, the low-temperature economizer water flow regulating valve adjusts the flue gas temperature at the outlet of the low-temperature economizer, and the low-pressure inlet water intake regulating valve and the booster circulation pump jointly adjust the economizer inlet water temperature; The outlet flue gas temperature of each low-temperature economizer is controlled by a low-temperature economizer water flow regulating valve. Multiple flue gas measuring points are arranged at the outlets of the four low-temperature economizers, and the median value of the multiple measuring points is taken. Considering that the long-term low-temperature operation of the flue gas will cause low-temperature corrosion to the pipe wall, the four selected outlet flue gas temperature measuring points are passed through a small selection controller to obtain the minimum flue gas temperature value as the controlled object of the first PID controller. The control setting value of the outlet flue gas temperature is the low-temperature economizer outlet flue gas temperature setting value, which is realized by manual setting by the operator. The first PID controller includes proportional action and integral action. When the outlet flue gas temperature of the low-temperature economizer is When the minimum value increases, a positive deviation occurs between the actual minimum value of the low-temperature economizer flue gas temperature and the set value signal of the low-temperature economizer outlet flue gas temperature, so that the proportional action and integral action of the first PID controller start to act, and an instruction to close the low-temperature economizer water volume regulating valve is issued, thereby lowering the flue gas temperature by lowering the water temperature; similarly, when the minimum value of the low-temperature economizer outlet flue gas temperature decreases, a negative deviation occurs between the actual minimum value of the low-temperature economizer flue gas temperature and the set value signal of the low-temperature economizer outlet flue gas temperature, so that the proportional action and integral action of the first PID controller start to act, and an instruction to open the low-temperature economizer water volume regulating valve is issued, thereby raising the flue gas temperature by raising the water temperature; In order to prevent the maximum value of the outlet flue gas temperature from being too high, the four outlet flue gas temperature measurement points that have been screened out will be passed through the general controller to obtain the maximum flue gas temperature value. Under abnormal working conditions, when the maximum flue gas temperature value of the low-temperature economizer is 3℃--6℃ greater than the set value of the low-temperature economizer outlet flue gas temperature, the low-temperature economizer outlet flue gas temperature set value will be slightly corrected downward through the adder to form the final low-temperature economizer outlet flue gas temperature control set value to enter the adjustment; Considering the load command change condition of the unit, the first differential controller will be used to advance the low-temperature economizer water flow regulating valve command; when the unit load command increases, the flue gas volume and flue gas temperature will increase. At this time, the first differential controller will directly give the command to close the low-temperature economizer water flow regulating valve to maintain the temperature stability; when the unit load command decreases, the flue gas volume and flue gas temperature will decrease. At this time, the first differential controller will directly give the command to open the low-temperature economizer water flow regulating valve to maintain the temperature stability; Finally, considering that the low-temperature economizer water flow regulating valve is the main regulating valve for the deaerator, it is necessary to ensure that the entire unit has sufficient feed water flow. The minimum flow protection link is designed. When the actual feed water flow is lower than the preset feed water flow value, the low-temperature economizer water flow regulating valve is prohibited from continuing to close; The low-temperature economizer inlet water temperature is jointly regulated by a booster circulation pump and a low-pressure inlet water intake regulating valve. A plurality of measuring points are arranged at the low-temperature economizer inlet water temperature measuring point (12), and an average value is taken for the plurality of measuring points. When the unit is operated in a low-load section, the inlet water temperature is relatively low. At this time, the booster circulation pump is used for regulation. The regulation is regulated by a third PID controller, including proportional action and integral action. When the low-temperature economizer inlet water temperature measuring point increases, a positive deviation occurs between the actual inlet water temperature of the low-temperature economizer and the low-temperature economizer inlet water temperature set value signal, so that the proportional action and integral action of the third PID controller start to act, and an instruction to turn off the booster circulation pump is issued to meet the water temperature requirement. Similarly, when the low-temperature economizer inlet water temperature measuring point decreases, a negative deviation occurs between the actual inlet water temperature of the low-temperature economizer and the low-temperature economizer inlet water temperature set value signal, so that the proportional action and integral action of the third PID controller start to act, and an instruction to turn on the booster circulation pump is issued to meet the water temperature requirement. At the same time, when the unit load command changes, the second differential controller will also be used to advance the command of the boost circulation pump to meet the temperature requirement; when the unit load command increases, the flue gas volume and flue gas temperature will increase, and the second differential controller will directly give the command to turn off the boost circulation pump to meet the temperature requirement; when the unit load command decreases, the flue gas volume and flue gas temperature will decrease, and the second differential controller will directly give the command to turn on the boost circulation pump to meet the temperature requirement; When the unit is running from low load to high load, as the water temperature rises, the booster circulation pump will gradually close. When it is closed to 5% opening, if the low-temperature economizer inlet water temperature measurement point is still higher than the low-temperature economizer inlet water temperature setting value, it means that the booster circulation pump has no adjustment margin, and the system automatically switches to the low-pressure inlet water intake regulating valve to continue to adjust the low-temperature economizer inlet water temperature measurement point; the adjustment is adjusted by the second PID controller, including proportional action and integral action; When the low-temperature economizer inlet water temperature measuring point increases, a positive deviation occurs between the actual low-temperature economizer inlet water temperature and the low-temperature economizer inlet water temperature set value signal, so that the proportional action and integral action of the second PID controller start to act, and an instruction to open the low-temperature addition inlet water intake regulating valve is issued to meet the water temperature demand; similarly, when the low-temperature economizer inlet water temperature measuring point decreases, a negative deviation occurs between the actual low-temperature economizer inlet water temperature and the low-temperature economizer inlet water temperature set value signal, so that the proportional action and integral action of the second PID controller start to act, and an instruction to close the low-temperature addition inlet water intake regulating valve is issued to meet the water temperature demand; At the same time, when the unit load command changes, the differential controller will also act in advance to act on the low-pressure inlet water intake regulating valve command to meet the temperature requirement; when the unit load command increases, the flue gas volume and flue gas temperature will increase, and the differential controller will directly give an instruction to open the low-pressure inlet water intake regulating valve 7 to meet the temperature requirement; when the unit load command decreases, the flue gas volume and flue gas temperature will decrease, and the differential controller will directly give an instruction to close the low-pressure inlet water intake regulating valve to meet the temperature requirement; When the unit switches from high load to low load operation, the low-pressure inlet water intake regulating valve gradually closes. When it is closed to the lower limit, if the low-temperature economizer inlet water temperature measuring point is still lower than the low-temperature economizer inlet water temperature setting value, it indicates that the low-pressure inlet water intake regulating valve has no adjustment margin, and the system automatically switches to the boost circulation pump to continue to adjust the low-temperature economizer inlet water temperature measuring point.

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