CN115309201A - Automatic control method for inlet flue gas temperature of denitration system of thermal power plant boiler - Google Patents
Automatic control method for inlet flue gas temperature of denitration system of thermal power plant boiler Download PDFInfo
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8621—Removing nitrogen compounds
- B01D53/8625—Nitrogen oxides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8696—Controlling the catalytic process
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/90—Injecting reactants
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/02—Other waste gases
- B01D2258/0283—Flue gases
Abstract
A flue gas bypass adjusting baffle is installed on a flue gas bypass of a boiler economizer of a thermal power plant, a flue gas forward path adjusting baffle is installed at an outlet of the economizer, a temperature element is installed at an inlet of a denitration device to measure the temperature of the flue gas, a set value of the inlet flue gas temperature of the denitration system is set, and under the automatic state of the control system, the deviation of the measured value and the set value is controlled by an instruction output by a PID control algorithm and the opening degrees of the flue gas bypass adjusting baffle and the flue gas forward path adjusting baffle are controlled by an executing mechanism. The invention is suitable for automatically controlling the inlet flue gas temperature of the denitration system of the boiler of the thermal power plant under the low-load working condition, realizes the functions by computer control equipment such as a DCS (distributed control system), a Programmable Logic Controller (PLC) and the like, brings great convenience to the use, greatly reduces the labor intensity of personnel, also reduces the possibility of pollutant emission exceeding caused by misoperation of the personnel, and has strong adaptability and reliability.
Description
Technical Field
The invention relates to the technical field of thermal power generation.
Background
In recent years, with the stricter environmental requirements, almost all the boiler equipment and systems of each unit of the thermal power plant are modified to meet the emission standards of pollutants. Desulfurization and dust collecting equipment are operated at full load of a random set, and a denitration system cannot be put into full load due to the chemical reaction principle.
At present, the mature flue gas denitration technology widely used in the boiler of a coal-fired power plant is a Selective Catalytic Reduction (SCR) technology, in the whole boiler flue gas flow, the heating surface of the last-stage boiler before an air preheater is an economizer, and the aim of reducing the inlet flue gas temperature of the preheater and saving the coal consumption is achieved. The denitration system is arranged between the economizer and the preheater, the catalyst adopted by the selective catalytic reduction reaction usually has the working temperature range of 300-400 ℃, and the catalyst cannot play the proper role when the temperature range is exceeded. In conventional boiler designs, the following problems can exist: when the load of the unit is high, the inlet smoke temperature of the denitration system is just in the normal operation range of the catalyst; and when the unit load is lower, the inlet flue gas temperature of the denitration system is lower than the normal use temperature of the catalyst. If the design smoke temperature of the inlet of the denitration system is increased to meet the requirement of the catalyst under the condition of low load, the smoke temperature is higher under the condition of high load, the exhaust gas temperature is high, the boiler efficiency is low, and the coal consumption is large. Therefore, the design is generally performed so as to satisfy a low exhaust gas temperature at a high load, which causes the power station to operate only by disconnecting the denitration system at a low load, and does not meet the requirement of the latest index of emission of nitrogen oxides.
In order to solve the contradiction that the inlet flue gas temperature of the denitration system at a low-load time interval does not meet the working conditions of the catalyst, four schemes are generally adopted for increasing the flue gas temperature at the inlet of the denitration system in each power station at present, namely, a bypass flue is arranged, a coal economizer bypass is arranged, the coal economizer is modified in a grading way, and regenerative steam extraction is used for supplementing water and heating, wherein the first two methods are most commonly used. The technology is researched and invented for realizing automatic control of the bypass flue after the adjusting baffle is installed on the bypass flue, so that the requirement that the inlet flue gas temperature of a denitration system meets the low-load operation of a boiler is met, the safe and stable operation of equipment is ensured, and the continuous investment of the denitration system is also ensured.
In actual engineering construction, a hole is formed in a flue at the inlet of the economizer, and a part of flue gas is pumped to the inlet of a denitration system, namely a bypass flue 2 of the economizer, as shown in fig. 1. When the boiler operates at low load, the flue gas at the inlet of the denitration system at low load reaches above 320 ℃ by extracting the flue gas with higher temperature and mixing the flue gas with the flue gas from the outlet of the economizer. In the prior art, an electric adjusting baffle (hereinafter referred to as a flue gas forward path adjusting baffle and a flue gas bypass adjusting baffle for short) is additionally arranged on an outlet of an economizer and a bypass flue so as to adjust the temperature of flue gas at an inlet of a denitration system.
Adopt bypass baffle 3 adjustment although can play the effect that improves denitration system import department gas temperature, most power plants adopt manual control at present, need in time carry out manual operation adjustment when load changes. Even if automatic control is adopted, in the low-load period of the boiler, the adjusting speed of the bypass baffle 3 and the forward baffle 5 is low, the accuracy is low, the inlet temperature reaction of the denitration system is low, the adaptation range of the unit load is not wide, large control deviation exists when the unit load is rapidly changed, and the probability of manual misoperation is high due to the fact that the two baffles are opposite in action direction when adjusted, and potential safety hazards exist.
Disclosure of Invention
The invention provides an automatic control method for inlet flue gas temperature of a denitration system of a boiler of a thermal power plant, aiming at solving the technical problems that in the prior art, the inlet temperature of the denitration system cannot be automatically controlled or the inlet temperature of the denitration system is slow in response time, large in control deviation, high in risk of human intervention and the like after being automatically controlled.
The technical scheme adopted by the invention for realizing the purpose is as follows: a flue gas bypass adjusting baffle 3 is installed on a flue gas bypass 2 of a boiler economizer 1, a flue gas forward adjusting baffle 5 is installed at an outlet of the economizer 1, a temperature element is installed at an inlet of a denitration device 4 to measure the temperature of the flue gas, a set value of the flue gas temperature at the inlet of the denitration system is set, and the deviation of the measured value and the set value is controlled by an instruction output by a PID control algorithm and an actuating mechanism to control the opening degrees of the flue gas bypass adjusting baffle 3 and the flue gas forward adjusting baffle 5 under an automatic state of the control system.
When the boiler operates in a load working condition of 60 percent or above, the temperature of the flue gas at the inlet of the denitration system meets a set value required by the denitration system, the bypass baffles are all closed, the position feedback is 0 percent, the flue gas forward path adjusting baffles 5 are all opened, the position feedback is 100 percent, and the flue gas all passes through the economizer; when the system is in an automatic state, if the measured value of the inlet flue gas temperature of the denitration system is lower than the set value, the instruction output by the PID control algorithm firstly controls the bypass adjusting baffle 3 to increase the opening, if the bypass adjusting baffle 3 is completely opened, the inlet flue gas temperature of the denitration system is still lower than the set value required by the system, the forward adjusting baffle 5 starts to be closed to improve the inlet flue gas temperature of the denitration system, until the set value is equal to the measured value, the system stops adjusting, and if the measured value of the inlet flue gas temperature of the denitration system is higher than the set value required by the system, the automatic system acts in the opposite direction.
Proportional and offset operations are respectively carried out on the instructions output by the PID control algorithm, the calculation results are used as control instructions of the flue gas bypass adjusting baffle 3 and the flue gas main path adjusting baffle 5,
dividing an instruction C output by a PID control algorithm into two sections, wherein the first section is 0-50 and serves as a bypass baffle working section, the second section is 50-100 and serves as a flue gas forward path adjusting baffle 5 working section, the first section serves as a bypass baffle working section, when C is changed from 0 to 50, the bypass adjusting baffle 3 is gradually opened, namely an opening instruction C Bypass path From 0 to 100, so the first stage C Bypass path =2 × C, the scaling factor of the control command of the bypass adjusting damper 3 is 2;
the second section is used as a forward baffle working section, and when C is changed from 50 to 100, the smoke forward adjusting baffle (5) is gradually closed, namely an opening instruction C Road for straight line Changing from 100 to 0, in the second phase, let the scale factor be K, the offset be B, when C =50, C Road for correction =100, giving formula 1, when C =100, C Road for correction =0, and then equation 2 is obtained, and equation 1 and equation 2 form an equation system as follows
K × 50 B=100 (formula 1)
K × 100 B=0 (formula 2)
K = -2,b = -200 is calculated, so the scale factor of the forward damper control command is-2, the offset is 200;
because the opening instructions of the flue gas forward path adjusting baffle 5 and the bypass adjusting baffle 3 can only be 0-100%, the finally output instruction value is limited between 0 and 100, and after the C is subjected to sectional treatment, the sectional control of the bypass baffle and the forward path baffle is realized.
The automatic system is in the manual state, the two regulating baffles can receive different opening instructions from operators, manual regulation is carried out manually, in the automatic state, the manual set values of the two baffles need to change along with the change of the feedback values of the two baffle valve positions on site, in the manual state, the set values of the system need to change along with the change of the real-time measured values of the regulated quantity, and the control system can track the correct tracking value through the judgment of the opening instruction C; in the automatic state of the system, when the opening instruction C is less than 50%, the manual set value is judged to be the working section of the bypass baffle, the manual set value is required to change along with the change of the feedback value of the valve position of the on-site bypass baffle, and when the opening instruction C is more than 50%, the manual set value is judged to be the working section of the forward baffle, and the manual set value is required to change along with the change of the feedback value of the valve position of the on-site forward baffle.
At least 3 temperature elements are arranged at the inlet of the denitration device 4 to measure the temperature of the flue gas, a DCS is introduced, and the average value of three measured values is taken as the regulated value of the automatic control system.
The automatic control method for the inlet flue gas temperature of the denitration system of the thermal power plant boiler is suitable for automatically controlling the inlet flue gas temperature of the denitration system of the thermal power plant boiler under the low-load working condition, the functions of the automatic control method are realized through computer control equipment such as a DCS (distributed control system), a Programmable Logic Controller (PLC) and the like, great convenience is brought to use, the labor intensity of personnel is greatly reduced, the possibility that pollutant emission exceeds the standard due to misoperation of the personnel is reduced, and the automatic control method for the inlet flue gas temperature of the denitration system of the thermal power plant boiler has strong adaptability and reliability.
Drawings
FIG. 1 is a diagram of an economizer plus bypass stack system of the present invention.
FIG. 2 is a SAMA diagram of an automatic inlet temperature control system for a denitration system according to the present invention.
In the figure: 1. economizer, 2, flue gas bypass, 3, flue gas bypass adjusting plate, 4, denitrification facility, 5, flue gas positive way adjusting plate, 6, flue gas positive way.
Detailed Description
Because the cross-sectional area of the outlet flue of the general power station boiler economizer is larger, two or more actuating mechanisms can be adopted to drive the forward baffle, but the two or more forward baffles need to receive the same instruction. The positive way baffle keeps opening completely when the boiler normal operating, and when the boiler was moved under the low-load operating mode, the deNOx systems entry flue gas temperature began to descend, and automatic system can make bypass baffle and positive way baffle adjust according to the control needs this moment, guarantees under the prerequisite of bypass flue gas flow regulation continuity, reduces the heat transfer of economizer, improves the deNOx systems entry temperature, guarantees the continuous steady operation of deNOx systems. The configuration of Control logic is performed in a Distributed Control System (DCS) of the generator set, and a Control function is implemented by using a single-loop PID (proportional, integral, and derivative Control algorithm) and corresponding logic function blocks, and the specific method is as follows:
as shown in fig. 2, the boiler economizer is provided with a bypass flue and an adjusting baffle (i.e. a flue gas bypass adjusting baffle 3) is installed on the bypass flue, and under the condition that an adjusting baffle (i.e. a flue gas forward adjusting baffle 5) is installed at the outlet of the economizer, the automatic control method for the inlet flue gas temperature of the denitration system under the low-load working condition of the boiler is as follows:
(1) General architecture of automatic control system design:
at least 3 temperature elements are arranged at proper positions of an inlet of the denitration system to measure the temperature of the flue gas, the flue gas is introduced into a DCS, and the average value of three measured values is taken as the regulated quantity of the automatic control system. And manually setting a set value of the inlet flue gas temperature of the denitration system by an operator. Under the automatic state of the control system, the deviation between the measured value and the set value is controlled by the instruction output by the PID control algorithm to control the opening degrees of the bypass baffle and the forward baffle. In the manual state of the automatic system, the two adjusting baffles can receive different opening instructions from operators to manually adjust.
(2) Designing the control function of the automatic control system:
when the boiler generally operates under the load working condition of 60 percent or more, the temperature of the flue gas at the inlet of the denitration system meets the set value required by the denitration system. At the moment, the bypass baffles are completely closed, namely the position feedback is 0%, the forward baffle is completely opened, namely the position feedback is 100%, and the flue gas completely passes through the economizer.
When the system is in an automatic state, if a measured value of the inlet flue gas temperature of the denitration system is lower than a set value, an instruction output by a PID control algorithm firstly controls a bypass baffle to increase the opening, if the bypass baffle is completely opened (position feedback is 100%), the inlet flue gas temperature of the denitration system is still lower than the set value required by the system, a forward baffle is started to be closed (the lowest position is set to be 30% to avoid complete closing), a bypass flue of an economizer is forced to increase the flue gas flow, the heat exchange quantity of the economizer is further reduced, the inlet flue gas temperature of the denitration system is increased, and the system stops adjusting until the set value is equal to the measured value and is stabilized under a certain working condition. If the measured value of the inlet flue gas temperature of the denitration system is higher than the set value required by the system, the automatic system acts in the opposite direction.
(3) Designing and calculating the proportion and the offset of control commands of the bypass baffle and the forward baffle:
the automatic system uses a PID algorithm to control the bypass baffle and the main baffle, under the same working condition, the adjusting directions of the two baffles are opposite and have a sequence, so that the proportional and offset operation is respectively carried out on the instruction output by the PID algorithm, namely, the calculation result is used as the control instruction of the bypass baffle and the main baffle. And dividing an instruction C output by the PID control algorithm into two sections, wherein the first section is 0-50 and is used as a bypass baffle working section, and the second section is 50-100 and is used as a forward baffle working section. The process specification is changed from 0 to 100 with the PID control algorithm output.
The first section is used as the bypass damper working section, when C changes from 0 to 50, the bypass damper should be opened gradually, namely, the opening command C Bypass path From 0 to 100, so the first stage
C Bypass path =2×C
The scale factor of the bypass damper control command is 2.
The second section is made ofFor the forward baffle operating section, the forward baffle should be gradually closed when C is changed from 50 to 100, i.e. the opening command C Road for straight line From 100 to 0, so in the second phase, let the scaling factor be K, the offset be B, and when C =50, C Road for straight line =100, giving formula 1, when C =100, C Road for correction =0, and then equation 2 is obtained, and equation 1 and equation 2 form an equation system as follows
K × 50 B=100 (formula 1)
K × 100 B=0 (formula 2)
K = -2,b = -200 is calculated, so the scale factor for the forward damper control command is-2 and the offset is 200.
The opening commands of the forward baffle and the bypass baffle can only be 0% to 100%, and the final output command value is limited to be 0 to 100. After the C is subjected to sectional treatment, the sectional control of the bypass baffle and the forward baffle is realized.
(4) And (3) tracking the position of a baffle when the automatic control system is manually and automatically switched:
the automatic control system should keep the output signal of the controller from sudden change at the moment of manual and automatic switching so as to avoid the switching from interfering with the control system and the actuating mechanism. In an automatic state, the manual set values of the two baffles need to change along with the change of the feedback values of the two baffle valve positions on site; in the manual state, the system setting value is changed along with the change of the real-time measurement value of the modulated quantity. Through the judgment of C, the control system can track the correct tracking value. In the automatic state of the system, when C is less than 50%, the bypass baffle working section is judged, and the manual set value is required to change along with the change of the feedback value of the valve position of the on-site bypass baffle. When C is more than 50%, the working section of the road sign is judged, the manual set value is changed along with the change of the feedback value of the valve position of the road sign on site, and the set value of the automatic system is tracked according to the rule in the manual state.
When the main baffle and the bypass baffle are both automatically controlled, the whole system enters an automatic working state, and after any one baffle is manually operated, the whole system is forcibly controlled manually.
The invention automatically controls the bypass baffles arranged on the coal economizer outlet forward baffle and the bypass flue according to logic, completes the automatic coordination control of the two baffles in time sequence and direction through the additional calculation of proportional bias under the instruction output by a PID control algorithm, simultaneously, the system logic can automatically judge the current working section of the system, can accurately realize the set value tracking function under abnormal working conditions, and ensures the undisturbed switching of the system between manual and automatic states. Through on-site actual observation and experiment, the amplification factor and the integral time in the PID control algorithm are properly adjusted, and on the premise of ensuring the safe operation of the boiler air and smoke system, the continuous and quick response of the inlet temperature system of the denitration system during the variable load period of the boiler can be realized. Due to the introduction of the integral effect, the steady-state error of the inlet flue gas temperature of the denitration system can be controlled to be +/-1 ℃. Therefore, the technical problem of continuous and reliable input of the denitration system inlet temperature automatic system in the low-load state of the boiler is solved.
The present invention has been described in terms of embodiments, and it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (5)
1. The automatic control method for the inlet flue gas temperature of the denitration system of the boiler of the thermal power plant is characterized by comprising the following steps of: a flue gas bypass adjusting baffle (3) is installed on a flue gas bypass (2) of a boiler economizer (1), a flue gas forward adjusting baffle (5) is installed at an outlet of the economizer (1), a temperature element is installed at an inlet of a denitration device (4) to measure the temperature of the flue gas, a set value of the inlet flue gas temperature of a denitration system is set, and a control system controls the opening degrees of the flue gas bypass adjusting baffle (3) and the flue gas forward adjusting baffle (5) through an instruction output by a PID control algorithm and an execution mechanism under an automatic state.
2. The automatic control method for the inlet flue gas temperature of the denitration system of the thermal power plant boiler as claimed in claim 1, characterized in that: when the boiler operates under the load working condition of 60 percent or more, the temperature of the flue gas at the inlet of the denitration system meets the set value required by the denitration system, the bypass baffles are all closed, the position feedback is 0 percent, the flue gas positive path adjusting baffles (5) are all opened, the position feedback is 100 percent, and the flue gas all passes through the economizer; when the system is in an automatic state, if a measured value of the inlet flue gas temperature of the denitration system is lower than a set value, an instruction output by a PID control algorithm firstly controls the bypass adjusting baffle (3) to increase the opening, if the bypass adjusting baffle (3) is completely opened, the inlet flue gas temperature of the denitration system is still lower than the set value required by the system, the forward adjusting baffle (5) starts to be closed to improve the inlet flue gas temperature of the denitration system until the set value is equal to the measured value, the system stops adjusting, and if the measured value of the inlet flue gas temperature of the denitration system is higher than the set value required by the system, the automatic system acts in the opposite direction.
3. The automatic control method for the inlet flue gas temperature of the denitration system of the thermal power plant boiler as claimed in claim 2, characterized in that: proportional and offset operation is respectively carried out on the instructions output by the PID control algorithm, the calculation result is used as the control instruction of the flue gas bypass adjusting baffle (3) and the flue gas forward path adjusting baffle (5),
dividing an instruction C output by a PID control algorithm into two sections, wherein the first section is 0-50 and serves as a bypass baffle working section, the second section is 50-100 and serves as a flue gas forward path adjusting baffle (5) working section, the first section serves as a bypass baffle working section, when the C is changed from 0 to 50, the bypass adjusting baffle (3) is gradually opened, namely an opening instruction C Bypass path From 0 to 100, so the first stage C Bypass path =2 × C, the scale factor of the control command of the bypass adjusting damper (3) is 2;
the second section is used as a normal baffle working section, and when C is changed from 50 to 100, smoke is generatedThe gas positive path adjusting baffle (5) is gradually closed, namely an opening instruction C Road for correction Changing from 100 to 0, in the second phase, let the scale factor be K, the offset be B, when C =50, C Road for correction =100, resulting in formula 1, when C =100, C Road for correction =0, and then equation 2 is obtained, and equation 1 and equation 2 form an equation system as follows
K × 50 B=100 (formula 1)
K × 100 B=0 (formula 2)
K = -2,b = -200 is calculated, so the scale factor of the forward damper control command is-2, the offset is 200;
because the opening instructions of the flue gas main path adjusting baffle (5) and the bypass adjusting baffle (3) can only be 0-100%, the finally output instruction value is limited between 0 and 100, and after the C is subjected to sectional treatment, the sectional control of the bypass baffle and the main path baffle is realized.
4. The automatic control method for inlet flue gas temperature of a denitration system of a boiler of a thermal power plant according to claim 1, characterized in that: the automatic system is in the manual state, the two regulating baffles can receive different opening instructions from operators, manual regulation is carried out manually, in the automatic state, the manual set values of the two baffles need to change along with the change of the feedback values of the two baffle valve positions on site, in the manual state, the set values of the system need to change along with the change of the real-time measured values of the regulated quantity, and the control system can track the correct tracking value through the judgment of the opening instruction C; in the automatic state of the system, when the opening instruction C is less than 50%, the manual set value is judged to be the working section of the bypass baffle, the manual set value is required to change along with the change of the feedback value of the valve position of the on-site bypass baffle, and when the opening instruction C is more than 50%, the manual set value is judged to be the working section of the forward baffle, and the manual set value is required to change along with the change of the feedback value of the valve position of the on-site forward baffle.
5. The automatic control method for inlet flue gas temperature of a denitration system of a boiler of a thermal power plant according to claim 1, characterized in that: at least 3 temperature elements are arranged at the inlet of the denitration device (4) to measure the temperature of the flue gas, the flue gas is introduced into a DCS, and the average value of three measured values is taken as the regulated quantity of the automatic control system.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110502122.0A CN115309201A (en) | 2021-05-08 | 2021-05-08 | Automatic control method for inlet flue gas temperature of denitration system of thermal power plant boiler |
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| CN202110502122.0A CN115309201A (en) | 2021-05-08 | 2021-05-08 | Automatic control method for inlet flue gas temperature of denitration system of thermal power plant boiler |
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Application publication date: 20221108 |