CN106949457B - Supercritical boiler platen superheater overtemperature control system and method - Google Patents

Abstract

A supercritical boiler platen superheater overtemperature control system and method comprises wall temperature sensors arranged on the walls of platen superheaters, an in-situ measuring device for receiving signals of the wall temperature sensors, a power station Distributed Control System (DCS) in communication connection with the in-situ measuring device, a first-stage monitoring loop and a second-stage monitoring loop which are connected with the in-situ measuring device and used for monitoring the wall temperature sensors, an over-fire air baffle plate controlled by the power station Distributed Control System (DCS) and connected with the first-stage monitoring loop, and a desuperheating water spray regulating valve connected with the second-stage monitoring loop; the first-stage monitoring loop comprises a first-stage speed limiting module, a first-stage amplitude limiting module, a first-stage OR operation module and a first-stage output pulse module, and the second-stage monitoring loop comprises a second-stage speed limiting module, a second-stage amplitude limiting module, a second-stage OR operation module and a second-stage output pulse module; the invention also discloses a control method of the system; the system and the method have important significance for improving the operation reliability of the thermal power plant, prolonging the service life of key equipment and reducing the maintenance cost.

Description

A supercritical boiler panel superheater overtemperature control system and method

technical field

The invention relates to the technical field of automatic control of thermal power plants, in particular to a supercritical boiler screen superheater overtemperature control system and method.

Background technique

Since the 1990s, my country has successively introduced a number of supercritical units from the United States, Russia, and Japan, and has gradually become the main body of my country's high-power thermal power units. By the end of 2011, my country has become the country with the most ultra-supercritical thermal power units. It marks that my country's power industry has entered the "ultra-supercritical era". However, the ultra (super) critical unit, due to its high steam-water parameters, is closer to the allowable limit of the material, and it is easy to cause unstable combustion of the boiler or imbalance of dynamic heat flow in the unsteady process such as fast changing working conditions, resulting in high temperature heating The over-temperature of the surface has caused a large number of serious accidents and problems such as the explosion of the heating surface of the boiler, which has a significant impact on the safety and stability of power production, and has become a major problem that plagues the power generation industry:

First of all, the temperature and pressure of the working fluid in the supercritical boiler panel superheater are very high, and they are arranged in the area with the highest flue gas temperature at the furnace outlet. Harsh, the temperature of the pipe wall of the heating surface is close to the limit service temperature of the metal material.

Second, although the outlet steam temperature of the screen superheater is maintained at the rated level after the steam temperature adjustment and cross-mixing under normal operating conditions, due to the uneven distribution of the furnace flue gas temperature and the flow in the heating surface tube, especially in the In the dynamic process, there are deviations in the internal and external parameters of the local heating surface. Under certain conditions, it is easy to cause local overheating and overtemperature on the heating surface, and even cause accelerated oxidation and tube burst.

Third, the operating environment of thermal power units under the condition of domestic power marketization has caused the fluctuation of coal quality in thermal power units in my country and the frequent and large frequency regulation and peak regulation required by the power grid, which aggravates the difficulty of regulation and control of supercritical boilers. A lot of field experience It is shown that the over-temperature of the wall temperature is mainly caused by the short-term over-temperature of the dynamic process. In addition to the design and installation conditions, the above factors are the most direct causes of the over-temperature of the metal wall of the heating surface.

Fourth, as domestic power plants pay more attention to supercritical boiler wall temperature over-temperature, a large number of wall temperature monitoring and measurement points are generally added. Some units have installed thousands of wall temperature measurement points, but they can basically only achieve over-temperature monitoring. After the alarm, it is impossible to achieve effective analysis and real-time processing of such a large number of wall temperature measurement points, and to achieve over-temperature early warning and prevention. There is no effective automatic control method available.

The current status of related technologies is as follows:

1. Current status of wall temperature monitoring technology

At present, there are three main technologies for monitoring the wall temperature of ultra (super) critical boilers:

(1) Direct measurement technology

It is very difficult to measure the internal wall temperature of the boiler. Generally, the method of welding the armored thermocouple or the porcelain sleeve thermocouple to the metal tube wall of the heating surface is used to measure the wall temperature. Due to the reasons such as swing and the high temperature of flue gas in the heating surface screen area, these measuring points have higher requirements on the installation of the contact effect, resulting in lower measurement accuracy. At the same time, the harsh environment causes the measuring points to be easily damaged. Compared with subcritical boilers, the inner wall temperature measurement of supercritical boilers is more difficult to measure and maintain because of its higher soda parameters.

Due to the above problems, it is relatively unreliable to install measuring points directly at the critical points of the fire-side pipe wall or the end of the fins and perform long-term monitoring and control based on these measuring points. Therefore, the existing direct wall temperature measurement is only for alarm prompts. , and then the operators will make relevant judgments and disposals.

(2) Indirect measurement method

The indirect measurement method of boiler wall temperature is mostly used in power plants to measure the thickness of the oxide layer on the inner wall of the tube. This method has the advantages of quantitative accuracy, rapid non-destructiveness, etc., but it is necessary to accurately measure the thickness of the oxide layer on the inner wall of the tube during the shutdown period, and then calculate Average level and approximate distribution of boiler wall temperature. The limitations of this type of method are also very obvious. First, this method cannot be used for online real-time monitoring, and it is of little significance for online early warning and over-temperature prevention of ultra (super) critical boilers; second, this method relies heavily on careful tube wall oxidation. Layer thickness measurement is complex and expensive.

(3) Online soft measurement method

The so-called soft measurement is a method of calculating the target of the measured parameter according to the model algorithm through other parameters according to the predetermined model. With the development of computer technology, soft sensor technology shows unique advantages for the measurement and implementation of unmeasurable variables or variables that are difficult to measure accurately in the production process. The core problem of soft measurement is the establishment of its model, that is, the establishment of the correlation model between the variable to be estimated and other directly measured variables.

There are various methods of soft-sensor modeling, and various methods intersect and merge with each other, so it is difficult to have a proper and comprehensive classification method. At present, soft sensing modeling methods generally include: mechanism modeling, regression analysis, state estimation, pattern recognition, artificial neural network, fuzzy mathematics, support vector machine, process tomography, correlation analysis, nonlinear system information processing technology, etc. Soft sensing technologies based on these methods have their own advantages, disadvantages and applicable scope. Some methods have been successfully applied in the field of soft sensing. Some are still immature.

2. Status Quo of Wall Temperature Prediction and Early Warning Technology

At present, the over-temperature is mainly monitored and alarmed by a large number of temperature measuring probes installed on the high-temperature heating surface. The wall temperature measurement result exceeds the preset alarm upper limit, that is, an alarm prompt is given to the operator, and the operator will deal with it. However, the current problem is that with such a large number of wall temperature measurement points, it is difficult to rely on manual analysis and monitoring, and only alarm handling after over-temperature can be achieved, and it is difficult to achieve over-temperature prediction and early warning. To achieve effective mitigation and prevention of wall temperature over-temperature.

To sum up, based on the wall temperature measurement points of the panel superheater of the power station boiler, the development of its wall temperature over-temperature control system and method is helpful for improving the safety of boiler equipment and the life of high-temperature heated components, reducing over-temperature and even tube bursting and other problems or problems. Accidents play an important role.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a supercritical boiler panel superheater overtemperature control system and method, which can improve the operation reliability of thermal power plants, prolong the life of key equipment, and reduce maintenance and repair costs. are of great significance.

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

A supercritical boiler panel superheater overtemperature control system, comprising a wall temperature sensor 2 installed on the tube wall of the panel superheater 1, an on-site measuring device 3 for receiving signals from the wall temperature sensor 2, and an on-site measuring device 3 The power station distributed control system DCS4 for communication connection, the first-level monitoring loop and the second-level monitoring loop for monitoring each wall temperature sensor 2 connected to the local measuring device 3, and the power station distributed control system DCS The burnout air baffle 13 connected with the primary monitoring circuit and the temperature reducing water spray valve 14 connected with the secondary monitoring circuit; the first monitoring circuit includes a primary speed limiting module 5, a primary amplitude limiting module 6, A first-level or arithmetic module 7 connected with the first-level speed limiting module 5 and the first-level amplitude limiting module 6, a first-level output pulse module 8 connected with the first-level or arithmetic module 7, and the second-level monitoring loop includes a second-level speed limiting module 9. The secondary limiting module 10 , the secondary OR operation module 11 connected with the secondary speed limiting module 9 and the secondary limiting module 10 , and the secondary output pulse module 12 connected with the secondary OR operation module 11 .

The on-site measuring device 3 detects the temperature measurement signal of the wall temperature sensor 2 installed on each metal tube wall of the panel superheater 1. On the one hand, the temperature of each wall temperature sensor 2 is sent to the power station distributed control system DCS 4 for use by communication. Display and alarm after over-temperature occurs; on the other hand, the output of each wall temperature sensor 2 is detected through the first-level speed limit module 5, the first-level limit module 6, the second-level speed limit module 9, and the second-level limit module 10. .

The screen superheater 1 is located at the top of the supercritical boiler furnace, and is composed of several slender and coiled metal tubes. The superheated steam flows in the metal tube of the screen superheater 1, and the outside of the tube receives the mixed convection heat exchange of the high temperature flue gas and the exhausted air and the radiation heat exchange of the combustion flame in the furnace, so as to realize the heating of the superheated steam. When the working conditions of the supercritical boiler change, the external heat received by the screen superheater 1 and the heat absorbed by the internal superheated steam will be unbalanced, resulting in the change of the metal tube wall temperature of the screen superheater 1 until a new equilibrium state is reached. , the temperature of the metal tube wall of the screen superheater 1 tends to a new equilibrium point. When the fluctuation of working conditions in the dynamic process, the uneven distribution of flue gas temperature and flow outside the pipe, and/or the uneven flow of steam in the pipe produce a large unbalance, the panel superheater 1 may have individual or local pipe walls. The temperature is overheated, and in severe cases, a large area of the tube wall may be overheated. Under the existing technical conditions, when the wall temperature sensor 2 installed on the wall of the panel superheater 1 exceeds the over-temperature alarm value corresponding to the material, the DCS system 4 connected to the on-site measuring device 3 will According to the comparison between the signal of each wall temperature sensor and the over-temperature alarm value, a wall temperature over-temperature alarm prompt is issued to prompt the operator to deal with it.

A supercritical boiler panel superheater overtemperature control system and method of the present invention automatically monitors the output signals of a large number of wall temperature sensors 2 installed in the panel superheater 1 . The monitoring loop is divided into two levels. The two-level monitoring loop captures the highest temperature in a large number of wall temperature sensors 2 through the first-level speed limit module 5 and the second-level speed limit module 9 and the first-level limit module 6 and the second-level limit module 10 respectively. and the fastest heating rate, when the output temperature or heating rate of any wall temperature sensor 2 exceeds the limit set at each level, the first-level OR operation module 7 and the second-level OR operation module 11 output to the first-level pulse output module 8 and the secondary pulse output module 12 to generate a control command signal increment to perform cooling control; among them, because the burnout air volume has a slight influence on the wall temperature of the panel superheater 1, the influence on the operation stability and economy of the generator set system is also relatively small. Soft, relatively speaking, the change of the desuperheating water spray amount has obvious influence on the wall temperature change of the panel superheater 1 and the operation stability and economy of the generator set system. Therefore, the limit value set by the primary monitoring loop If it is relatively low, the control output is superimposed on the control command of the exhaust air baffle 13, and the cooling of the screen superheater 1 is carried out by increasing the air volume of the gas turbine; On the warm water spraying door 14, the cooling of the panel superheater 1 is carried out by increasing the amount of cooling water spray; a slight over-temperature risk will trigger the first-level monitoring loop, and the panel superheater can be overheated by increasing the gas volume of the gas turbine. Temperature control, the more serious over-temperature risk will trigger the primary and secondary monitoring loops at the same time. Before the superheater 1 overheats, it automatically predicts the risk of overheating, and comprehensively utilizes the methods of increasing the air volume of the gas turbine and the amount of cooling water to achieve the goal of actively reducing the risk of overheating and avoiding overheating. occur, maintain the safety of the metal pipe of the screen superheater 1.

Compared with the prior art, the characteristics of the present invention are as follows:

(1) The existing technology cannot achieve effective monitoring and management for a large number of wall temperature measuring points installed on the boiler screen superheater, and can only realize the alarm after the wall temperature exceeds the temperature, and the operator can only make a post-event response, which is impossible Have the energy to fully monitor the wall temperature.

(2) On the basis of the hardware structure of the existing thermal power station system, there is no need for complex hardware equipment transformation, and the monitoring and control of the wall temperature of the boiler screen superheater can be realized only by adding the primary and secondary monitoring loops to achieve effective reduction. The purpose of shielding the risk of over-temperature over the wall temperature.

(3) The prior art adopts the burnout damper baffle for the control of combustion, and opening the large burnout damper can be used to reduce the loss of incomplete combustion, reduce the carbon content of fly ash, and reduce the generation of NOx, but the excessive burnout wind will reduce the combustion efficiency. When judging the risk of over-temperature, the invention realizes the purpose of assisting the reduction of the wall temperature of the screen with the help of the low-temperature burn-out wind in a short period of time, and further enriches the automatic control function of the burn-out wind baffle.

(4) In the prior art, the superheater desuperheating water spray is used to reduce the temperature of the superheated steam in the superheater in an emergency, so as to avoid the overtemperature and overpressure of the superheated steam, which threatens the safety of the superheater. When judging the risk of over-temperature, the invention realizes the purpose of assisting the reduction of the wall temperature of the screen by means of the cooling effect of the desuperheating water spray in a short time, and further enriches the automatic control function of the desuperheating water spray of the boiler superheater.

(5) Because the effect of the over-burning wind is mild and has little effect on the unit efficiency, it is used as a conventional means of over-temperature risk control; while the desuperheating water spray has a strong effect and has a greater impact on the unit efficiency, so it is used as an over-temperature risk. Use both when strong. Through the two-stage control function, the influence on the safety, stability and economy of the unit can be taken into account at the same time, and the over-temperature automatic protection of the screen superheater which is prone to over-temperature of the wall temperature can be realized. The solution of the problem is of great significance.

Description of drawings

FIG. 1 is a schematic diagram of the system structure of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

A supercritical boiler panel superheater overtemperature control system, comprising a wall temperature sensor 2 installed on the tube wall of the panel superheater 1, an on-site measuring device 3 for receiving signals from the wall temperature sensor 2, and an on-site measuring device 3 The power station distributed control system DCS4 for communication connection, the first-level speed limit module 5 for monitoring each wall temperature sensor 2, the first-level amplitude limit module 6, the first-level or operation module 7, the first-level output pulse module 8, the second-level limiter Speed module 9 , secondary limiting module 10 , secondary OR operation module 11 , secondary output pulse module 12 , burnout air baffle 13 and temperature reduction water spray gate 14 controlled by distributed control system DCS4 of the power station.

During the temperature change of each metal tube wall of the panel superheater 1, the on-site measuring device 3 detects the temperature measurement signal of the wall temperature sensor 2 installed on each metal tube wall of the panel superheater 1. The temperature of the sensor 2 is sent to the DCS system 4 for display and alarm after the occurrence of over-temperature; 10 detects the output of each wall temperature sensor 2 .

When the temperature of any wall temperature sensor 2 has not been over-temperature, but exceeds the lower limit amplitude set by the primary limiting module 6, such as 495°C, or the temperature change rate of any wall temperature sensor 2 exceeds the setting of the primary speed limiting module 5 When the lower speed limit value is 10°C/min, the output of the first-level OR operation module 7 is true, and triggers the first-level output pulse module 8 in the distributed control system DCS4 of the power station, and the original control command of the burnout air baffle 13 On the basis of superimposing the cooling control pulse output by the first-level output pulse module 8, the burnout air baffle 13 connected to the distributed control system DCS4 of the power station is controlled to be further opened to increase the burnout air flow at the top of the furnace, thereby reducing the flow rate through the screen. The flue gas temperature of the superheater 1 can alleviate or even avoid the overheating of the screen superheater 1.

When the temperature of any wall temperature sensor 2 further increases, although the over temperature has not yet occurred, it exceeds the higher limit amplitude set by the secondary limiting module 10, such as 500°C or the temperature change rate of any wall temperature sensor 2 exceeds two When the higher speed limit value set by the stage speed limit module 9 is 20°C/min, the output of the second stage OR operation module 11 is true, and the second stage output pulse module 12 in the distributed control system DCS4 of the power station is triggered to spray water during the temperature reduction. On the basis of the original control command of the regulating door 14, the cooling control pulse output by the secondary output pulse module 12 is superimposed, and the cooling and spraying water regulating door 14 connected to the distributed control system DCS4 of the power station is controlled to be further opened, and the reduction of the temperature entering the panel superheater 1 is increased. Warm water is sprayed, thereby rapidly reducing the temperature of the superheated steam in the panel superheater 1, and quickly alleviating or even avoiding the overheating of the panel superheater 1.

Claims (5)

1. a supercritical boiler screen type superheater overtemperature control system, is characterized in that: comprise the wall temperature sensor (2) that is installed on the screen type superheater (1) tube wall, receive the wall temperature sensor (2) signal The on-site measuring device (3), the power station distributed control system DCS (4) connected in communication with the on-site measuring device (3), and the monitoring device for monitoring each wall temperature sensor (2) connected with the on-site measuring device (3) The first-level monitoring circuit and the second-level monitoring circuit, the exhaust air baffle (13) connected with the first-level monitoring circuit controlled by the distributed control system DCS (4) of the power station, and the temperature reduction connected with the second-level monitoring circuit A water spray gate (14); the first-level monitoring loop includes a first-level speed limiting module (5), a first-level amplitude limiting module (6), a first-level speed limiting module (5) and a first-level amplitude limiting module (6) ) connected to the first-level or operation module (7), the first-level output pulse module (8) connected to the first-level or operation module (7), the second-level monitoring loop includes the second-level speed limit module (9), the second-level limiter Amplitude module (10), a second-level OR operation module (11) connected with the second-level speed limiting module (9) and the second-level limiter module (10), and a second-level output pulse connected with the second-level OR operation module (11) module (12). 2. A supercritical boiler panel superheater overtemperature control system according to claim 1, wherein the on-site measuring device (3) detects and is installed on each metal tube wall of the panel superheater (1). The temperature measurement signal of the wall temperature sensor (2), on the one hand, the temperature of each wall temperature sensor (2) is sent to the power station distributed control system DCS (4) by means of communication for display and alarm after over-temperature occurs; On the one hand, the output of each wall temperature sensor (2) is detected by a first-level speed limit module (5), a first-level limit module (6), a second-level speed limit module (9), and a second-level limit module (10). 3. a kind of supercritical boiler panel type superheater overtemperature control system according to claim 1, is characterized in that: described panel type superheater (1) is located at the top of supercritical boiler hearth, consists of several slender coiled Metal tube composition. 4. the control method of a kind of supercritical boiler screen superheater overtemperature control system described in any one of claim 1 to 3, it is characterized in that: a large number of wall temperature sensors ( 2) The output signal is automatically monitored. The monitoring circuit is divided into two levels: the first-level monitoring loop and the second-level monitoring loop. The two-level monitoring loops pass through the first-level speed limit module (5) and the second-level speed limit module (9). ) and the first-level limiting module (6) and the second-level limiting module (10) capture the highest temperature and the fastest heating rate among a large number of wall temperature sensors (2), when the output temperature of any wall temperature sensor (2) or When the heating rate exceeds the limit set at each level, the first-level OR operation module (7) and the second-level OR operation module (11) output to the first-level output pulse module (8) and the second-level output pulse module (12) to generate a control command The signal increment is used for cooling control; among them, because the burnout air volume has a slight influence on the wall temperature of the panel superheater (1), the influence on the operation stability and economy of the generator set system is also relatively soft. The change of the water spray amount has obvious influence on the wall temperature change of the panel superheater (1) and the operation stability and economy of the generator set system. Therefore, the limit amplitude value set by the primary monitoring loop is relatively low, and the control output is superimposed. On the control command of the exhaust air baffle (13), the screen superheater (1) is cooled by increasing the air volume of the gas turbine; the limit amplitude value set in the secondary monitoring loop is higher, and the control output is superimposed on the temperature reduction spray. On the water control door (14), the screen superheater (1) is cooled by increasing the cooling water spray amount; a slight over-temperature risk will trigger the first-level monitoring loop, and the screen superheating can be achieved by increasing the gas volume of the gas turbine. The more serious risk of over-temperature will trigger the primary and secondary monitoring loops at the same time. By increasing the gas volume of the gas turbine and the amount of desuperheating water, the over-temperature control of the panel superheater can be achieved together; Before the screen superheater (1) overheats, it automatically predicts the risk of overheating, and comprehensively utilizes the methods of increasing the air volume of the gas turbine and the amount of water sprayed to reduce the temperature to achieve the goal of actively reducing the risk of overheating in the screen, so as to avoid To prevent the occurrence of overheating, maintain the safety of the metal pipe of the screen superheater (1). 5. control method according to claim 4 is characterized in that: concrete method is as follows: When the temperature of any wall temperature sensor (2) has not been over-temperature, but exceeds the lower limit amplitude set by the primary limiting module (6) or the temperature change rate of any wall temperature sensor (2) exceeds the primary speed limit When the lower speed limit value is set by the module (5), the output of the primary OR operation module (7) is true, and triggers the primary output pulse module (8) in the distributed control system DCS (4) of the power station. On the basis of the original control command of the baffle (13), the cooling control pulse output by the first-stage output pulse module (8) is superimposed, and the exhaust air baffle (13) connected with the distributed control system DCS (4) of the power station is controlled to be further opened. , increase the burnout air flow at the top of the furnace, thereby reducing the temperature of the flue gas flowing through the screen superheater (1), alleviating or even avoiding the overheating of the screen superheater (1); When the temperature of any wall temperature sensor (2) further increases, although the overtemperature has not yet occurred, it exceeds the higher limiting amplitude set by the secondary limiting module (10) or the temperature change of any wall temperature sensor (2). When the speed exceeds the higher speed limit value set by the secondary speed limit module (9), the output of the secondary OR operation module (11) is true, and triggers the secondary output pulse module (12) in the distributed control system DCS (4) of the power station. ), superimpose the cooling control pulse output by the secondary output pulse module (12) on the basis of the original control command of the cooling water spray gate (14) to control the cooling water spray gate connected to the distributed control system DCS (4) of the power station (14) Further increase the temperature and increase the temperature-reducing water spray entering the panel superheater (1), thereby rapidly reducing the temperature of the superheated steam in the panel superheater (1), and quickly relieve or even avoid the appearance of the panel superheater (1). overheating.

Images