A method for monitoring and closed-loop control of boiler water wall slagging

Abstract

The application discloses a boiler water cooling wall slagging monitoring and closed-loop control method, comprising the following steps: step 1, modeling the water cooling wall temperature historical data measured by each water cooling wall slagging state monitoring and positioning sensor to obtain the theoretical temperature value of the water cooling wall cleaning in each soot-blowing area; step 2, constructing the relationship among the measured water cooling wall temperature, the theoretical temperature value of the water cooling wall cleaning and the water cooling wall slagging layer thermal resistance in each soot-blowing area, and calculating the minimum value of the water cooling wall slagging layer thermal resistance in each soot-blowing area; step 3, reflecting the slagging condition of the corresponding soot-blowing area by the water cooling wall slagging layer thermal resistance, and constructing the judgment basis of the slagging degree of each soot-blowing area and the corresponding soot-blowing strategy; and step 4, judging the slagging degree of each soot-blowing area in the boiler operation process based on the judgment basis of the slagging degree of each soot-blowing area, and issuing the soot-blowing instruction of the corresponding wall-type soot-blower by the DCS system. By using the application, the accurate positioning and closed-loop control of the water cooling wall slagging can be realized.

Description

Technical Field

[0001] This invention belongs to the field of coal-fired power plant boiler technology, and in particular relates to a method for monitoring and closed-loop control of slagging on boiler water-cooled walls. Background Technology

[0002] Currently, research on the identification of slag buildup on the water-cooled walls of coal-fired boilers mainly consists of theoretical calculation methods and measurement methods on the back-fire side of the water-cooled wall. These methods have shortcomings such as inaccurate calculations, high costs, or poor accuracy, and cannot accurately locate the slag buildup on the water-cooled wall.

[0003] Domestic scholars have conducted extensive research on the monitoring of contamination status of heating surfaces in coal-fired power plant boilers and the optimization of soot blowing. They have adopted different methods for monitoring the contamination status of heating surfaces, developed corresponding online monitoring and soot blowing optimization systems, and applied them to different types of coal-fired boilers.

[0004] For example, Chinese patent publication number CN111637478A discloses a furnace soot blowing method; Chinese patent document publication number CN112283689A discloses an online monitoring system for ash on the heating surface of a coal-fired power plant boiler and its detection method.

[0005] However, due to the lack of significant breakthroughs in monitoring technologies related to the contamination status of the heating surfaces inside coal-fired boilers, it is impossible to pinpoint the specific location and severity of slagging. As a result, the actual application of both "optimized soot blowing systems" and "intelligent soot blowing systems" in major coal-fired power plants is not ideal and falls far short of the ideal. Most power plants have not actually put similar systems into operation. Currently, almost all coal-fired power plants still adopt a relatively blind soot blowing mode and strategy of "on-time and shift" + "sequential control soot blowing".

[0006] Using the above soot blowing strategy will not achieve the effect of precise soot blowing as needed, and may cause problems of "overblowing" or "underblowing", affecting the safe operation of the unit. Summary of the Invention

[0007] This invention provides a method for monitoring and closed-loop control of slagging on boiler water-cooled walls. By controlling each wall-mounted sootblower through a DCS system, precise positioning and closed-loop control of slagging on the boiler water-cooled walls can be achieved, improving boiler safety, economic efficiency, and intelligent operation.

[0008] A method for monitoring and closed-loop control of slagging on boiler water-cooled walls, the system of which includes boiler water-cooled walls, water-cooled wall slagging status monitoring and positioning sensors, data acquisition modules, DCS systems and wall-mounted soot blowers;

[0009] Based on the installation location of the wall-mounted sootblowers, the water-cooled wall is divided into multiple sootblowing zones, the same number as the number of wall-mounted sootblowers, with each sootblower as the center. Each sootblowing zone includes water-cooled wall tubes, fins between the water-cooled wall tubes, and weld scars between the water-cooled wall tubes and fins. A water-cooled wall slag condition monitoring and positioning sensor is arranged within each sootblowing zone and connected to a data acquisition module for real-time monitoring of fin temperature. The data acquisition module receives data signals from the water-cooled wall slag condition monitoring and positioning sensor and transmits them to the DCS system. The DCS system receives signals from the data acquisition module, processes the data, and performs closed-loop control of each wall-mounted sootblower. The wall-mounted sootblowers, arranged within each sootblowing zone, operate according to the control commands of the DCS system to remove slag from the corresponding sootblowing zone.

[0010] The method includes the following steps:

[0011] Step 1: Model the historical temperature data of each water-cooled wall measured by the monitoring and positioning sensors for slagging status of each water-cooled wall to obtain the theoretical temperature value of the water-cooled wall during cleaning in each soot blowing area.

[0012] Step 2: Based on the principles of heat transfer, construct the measured temperature T of the water-cooled wall in each soot blowing zone. w Theoretical temperature value during water-cooled wall cleaning Thermal resistance R of slag layer on water-cooled wall s The relationship between the three factors was analyzed, and the minimum thermal resistance R of the water-cooled wall slag layer in each soot blowing area was calculated based on historical data. s-min ;

[0013] Step 3, using the thermal resistance R of the slag layer on the water-cooled wall s It reflects the slagging situation in the corresponding soot blowing area, and constructs the judgment criteria for the degree of slagging in each soot blowing area and the corresponding soot blowing strategy;

[0014] Step 4: During boiler operation, the slagging status monitoring and positioning sensors of each water-cooled wall measure the temperature of the corresponding water-cooled wall in real time, and further calculate the thermal resistance R of the slagging layer on the water-cooled wall. s Then, based on the criteria for judging the degree of slagging in each soot blowing area, the degree of slagging in each soot blowing area during boiler operation is judged.

[0015] When slag forms in a certain area of ​​the water-cooled wall and needs to be removed by the corresponding sootblower, the corresponding wall-mounted sootblower requests a sootblowing request. The DCS system then issues a sootblowing command to the corresponding wall-mounted sootblower, achieving closed-loop control while monitoring the slag formation status of the water-cooled wall.

[0016] After slagging occurs on the water-cooled wall, it becomes the thermal resistance between the high-temperature flue gas in the furnace and the water-cooled wall. The thicker the slagging layer, the greater the thermal resistance, and the worse the heat exchange effect between the high-temperature flue gas and the water-cooled wall. Correspondingly, the temperature measured by the water-cooled wall slagging status monitoring and positioning sensor is lower. However, the relationship between the two is not a simple linear one. The temperature measured by the water-cooled wall slagging status monitoring and positioning sensor is affected by boiler load, coal mill operation mode, flame center height, flue gas damper, feedwater temperature, etc.

[0017] To establish an accurate soot blowing model for each sensor, in practical applications, after the installation of the water-cooled wall slagging status monitoring and positioning sensors, historical data is collected over a long period of time to construct the slagging status judgment criteria for each sensor. The slagging location is determined by judging the slagging status of sensors at different locations, and the slagging status is used as the basis for precise positioning and closed-loop control of water-cooled wall slagging.

[0018] In step 2, the relationship between the measured temperature of the water-cooled wall in each soot blowing zone, the theoretical temperature during water-cooled wall cleaning, and the thermal resistance of the slag layer on the water-cooled wall is established, specifically as follows:

[0019]

[0020] In the formula, R s Thermal resistance of the slag layer on the water-cooled wall; The theoretical temperature value for cleaning water-cooled walls; T w Δt represents the measured temperature of the water-cooled wall; n represents the number of water-cooled wall tubes in the soot blowing area, which are uniformly arranged; q represents the mass flow rate of the working fluid inside the water-cooled wall tube, in kg / s; Δh represents the enthalpy increase of the working fluid at both ends of the water-cooled wall tube, in kJ / kg.

[0021] In step 3, the criteria for judging the degree of slagging in each soot blowing zone and the corresponding soot blowing strategy are established, specifically as follows:

[0022] The DCS system measures the thermal resistance R of the slag layer on the water-cooled wall in each soot blowing zone. s Perform real-time calculations when R s -R s-min If the slag density is <0.04 W / K and the SD after the last soot blowing is <10%, then the soot blowing area corresponding to this sensor has slight slag buildup, and the corresponding wall-mounted soot blower does not need to be soot blown. SD represents the standard deviation; when R s -R s-min If the value is >0.04W / K, and the percentage after the last soot blowing is 10% < SD < 40%, then there is slag buildup in the soot blowing area corresponding to this sensor, which needs to be removed by the corresponding wall-mounted soot blower. A soot blowing request should be issued to the corresponding soot blower. When R... s -R s-minIf the value is greater than 0.04 W / K and the SD is greater than 40% after the last soot blowing, then there is slag in the soot blowing area corresponding to this sensor, but it will fall off on its own during boiler operation, and the corresponding wall-mounted soot blower does not need to be soot blown.

[0023] Furthermore, the water-cooled wall slagging status monitoring and positioning sensor includes an armored thermocouple, an external furnace fixing base, and a thermocouple protective sleeve.

[0024] The external furnace mounting base is installed on the fins between two water-cooled wall tubes in each soot blowing area. One end of the thermocouple protective sleeve is fixed to the through threaded hole provided on the external furnace mounting base. The fins are provided with thermocouple mounting holes. The measuring end of the armored thermocouple passes through the thermocouple protective sleeve and the through threaded hole of the external furnace mounting base and is installed in the thermocouple mounting hole of the fin.

[0025] Furthermore, the external furnace mounting base is made of the same material as the fins, making welding and installation of the external furnace mounting base more convenient and secure.

[0026] Furthermore, the depth of the thermocouple mounting hole is 50% of the fin thickness, allowing installation to be performed while the boiler is running. Compared with existing technologies, this avoids the need for installers to enter the furnace during shutdown to install the furnace heat collectors, significantly improving the convenience and timeliness of installation. Moreover, since the thermocouple is installed in the thermocouple mounting hole on the fin, it will not come into direct contact with the harsh environment of high temperature and dust inside the furnace, significantly improving the service life of the thermocouple.

[0027] Furthermore, the thermocouple mounting hole is located between the two water-cooled wall tubes.

[0028] The radius of the arc surface on both sides of the external furnace fixing base is the same as the radius of the outer wall surface of the water-cooled wall tube. The arc surface fits tightly with the water-cooled wall tube. After fitting, there is a gap between the external furnace fixing base and the fin. The external furnace fixing base is welded to the fin by two connecting blocks.

[0029] To avoid affecting the safe operation of the water-cooled wall, welded connecting blocks are provided at both the upper and lower ends of the external furnace fixing base. During installation, the external furnace fixing base is installed only on the fins of the water-cooled wall through the welded connecting blocks.

[0030] Furthermore, to facilitate the disassembly of the components of the water-cooled wall slagging status monitoring and positioning sensor, the thermocouple protective sleeve is provided with external threads and internal threads at both ends, with the external thread at one end connected to the furnace external fixed base and the internal thread at the other end connected to the fastening sleeve.

[0031] The fastening sleeve has internal threads and connects to the thermocouple protective sleeve to secure the armored thermocouple. During installation, the armored thermocouple is passed through the fastening sleeve and the protective sleeve in sequence until it reaches the mounting hole of the fin, and then the threads of the fastening sleeve are tightened.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This invention divides the water-cooled wall into multiple soot blowing zones based on the location of the wall-mounted soot blower. A water-cooled wall slagging status monitoring and positioning sensor is installed in each zone. By constructing the wall temperature measured by each sensor, the thermal resistance of the slagging layer in the corresponding zone is obtained. The thermal resistance reflects the slagging status of different zones of the water-cooled wall, realizing the monitoring of the slagging status and the positioning of slagging in different zones of the water-cooled wall. Through automatic identification and automatic control, the soot blowing system and closed-loop control are realized. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a system used in a boiler water-cooled wall slagging monitoring and closed-loop control method according to an embodiment of the present invention.

[0035] Figure 2 This is a schematic diagram of the water-cooled wall in an embodiment of the present invention.

[0036] Figure 3 This is a schematic diagram of a water-cooled wall slagging status monitoring and positioning sensor in an embodiment of the present invention.

[0037] Figure 4 This is a graph showing three trends in the data measured by the water-cooled wall slagging status monitoring and positioning sensor in an embodiment of the present invention.

[0038] Figure 5 This is a graph showing the relationship between the data measured by the water-cooled wall slagging status monitoring and positioning sensor and the unit's power generation load in an embodiment of the present invention.

[0039] Figure 6 This is a trend diagram of the comprehensive thermal resistance of three typical water-cooled wall slag layers in an embodiment of the present invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0041] like Figure 1 As shown, a boiler water-cooled wall slagging monitoring and closed-loop control system includes a coal-fired boiler DCS system 1, a data acquisition module 2, a water-cooled wall 3, a wall-type soot blower 4, and a water-cooled wall slagging status monitoring and positioning sensor 5.

[0042] Specifically, the water-cooled wall 3 receives heat from boiler combustion to heat the steam medium inside the water-cooled wall tubes; the water-cooled wall slagging status monitoring and positioning sensor 5 is used to monitor the slagging status of different areas of the water-cooled wall 3 in real time online; the wall-type soot blower 4 is used to remove slag blocks from the water-cooled wall in the furnace at its corresponding position; the data acquisition module 2 is used to collect the data measured by the water-cooled wall slagging status monitoring and positioning sensor 5 and transmit the collected data to the DCS system 1; the DCS system 1 receives the data from the data acquisition module 2 and processes it, identifies and locates the slagging area of ​​the water-cooled wall 3 according to the soot blowing model, and automatically issues soot blowing commands to the corresponding soot blowers in the areas that need soot blowing.

[0043] After slagging occurs on the water-cooled wall 3, the thermal resistance between the flame and the water-cooled wall increases, and the temperature measured by the water-cooled wall slagging status monitoring and positioning sensor 5 will decrease as the thickness of the slagging layer increases. Historical data is accumulated, and the judgment criteria for each water-cooled wall slagging status monitoring and positioning sensor 5 are established based on different slagging states of the water-cooled wall, which serves as the basis for the precise positioning of water-cooled wall slagging and the implementation of the closed-loop control system.

[0044] like Figure 2 As shown, the water-cooled wall 3 includes fins 301, weld scars 302, water-cooled wall tubes 303, and thermocouple mounting holes 304.

[0045] like Figure 3 As shown, the water-cooled wall slagging status monitoring and positioning sensor 5 includes an armored thermocouple 501, a fastening sleeve 502, a slot 503, a thermocouple protective sleeve 504, and an external furnace fixing base 505.

[0046] The fixed base 505 is installed on the fins between two water-cooled wall tubes of the water-cooled wall 3. The thermocouple protective sleeve 504 is installed on the external fixed base 505 via external threads. The armored thermocouple 501 is inserted into the bottom of the thermocouple mounting hole 304 on the fin of the water-cooled wall 3 through the fastening sleeve 502, the thermocouple protective sleeve 504, and the external fixed base 505 in sequence. The fastening sleeve 502 is connected to the thermocouple protective sleeve 504 via external threads. The external fixed base 505 is installed by welding, and the remaining components are fixed by threads. It can be installed and replaced when the boiler is hot. The slot 503 can be used with a wrench for tightening installation.

[0047] Thermocouple mounting hole 304 has a depth of 50% of the thickness of fin 301, and the measuring end of armored thermocouple 501 extends into the bottom of thermocouple mounting hole 304.

[0048] The external furnace mounting base 505 is made of the same material as the fins 301. The same type of steel facilitates welding and ensures a firm installation, preventing the mounting base from falling off due to stress during boiler combustion changes.

[0049] The furnace external fixed base 505 is equipped with connecting blocks for welding at the top and bottom, which facilitates welding during installation. The welding position is only between the connecting block and the fin 301, avoiding safety issues such as tearing caused by the furnace external fixed base 505 to the water-cooled wall tube 303.

[0050] The radius of the arc surface on both sides of the furnace external fixed base 505 is the same as the radius of the outer wall of the water-cooled wall tube 303, ensuring that the fixed block and the water-cooled wall tube 301 fit tightly. After fitting, the fixed base and the fin 301 leave a certain gap to eliminate the influence of weld scar 302 on welding.

[0051] The external furnace mounting base 505 is provided with threaded through holes, which facilitates the installation and removal of the thermocouple protection sleeve 504 during boiler hot operation.

[0052] The thermocouple protection sleeve 504 has internal and external threads at both ends. The external thread is connected to the internal thread of the furnace external fixed base 505, and the internal thread is connected to the fastening sleeve 502.

[0053] There are a large number of wall-mounted soot blowers 4 in coal-fired boilers. The water-cooled wall slagging status monitoring and positioning sensor 5 corresponds to each wall-mounted soot blower 4. In order to facilitate installation and subsequent management, the data of all water-cooled wall slagging status monitoring and positioning sensor 5 are first connected to the data acquisition module 2 and then uniformly transmitted to the DCS system 1.

[0054] The process of using this invention for slagging monitoring and closed-loop control is as follows:

[0055] Step 1: Based on the installation location of the wall-mounted sootblower in the coal-fired boiler, divide the water-cooled wall into areas equal to the number of sootblowers, with each sootblower as the center, and pinpoint the location of slagging to each area.

[0056] Step 2: Based on the layout of the wall-type soot blowers in the coal-fired water-cooled wall, divide the water-cooled wall into areas with the same number of soot blowers as the center, and install water-cooled wall slagging status monitoring and positioning sensors 5 within the soot blowing range of the soot blowers in different areas.

[0057] like Figure 4 As shown, the trend of data changes measured by sensor 5 for monitoring and locating slagging status of water-cooled walls is as follows:

[0058] Typical trend 1: Temperature T measured by the sensor w The temperature remained almost unchanged throughout the boiler's operation, with only a slight increase during soot blowing, ΔTw ≈ 10–20℃. At other times, the temperature measured by the sensor was constant. w It also fluctuates relatively little, almost appearing as a straight line;

[0059] Typical Trend 2: Temperature T measured by the sensor w It exhibits a certain periodic pattern of change, under the blowing action Tw The temperature rose rapidly, reaching approximately 550°C, with a ΔTw ≈ 100–120°C. The ΔT value increased significantly after several soot blowing actions. w Quite similar, after the blowing motion, T w Gradually decrease, and at T w It reaches a stable state at approximately 450℃.

[0060] Typical trend 3: Temperature T measured by the sensor w It exhibits a clear and frequent trend of irregular changes, with the temperature rise ΔT under the soot blowing action being significant. w ≈90~100℃, after the soot blowing action, T w The temperature drops rapidly by about 120-180°C, falling below about 400°C, with a relatively obvious temperature jump occurring every 2-4 hours. Within a 24-hour soot blowing cycle, the temperature jumps about 10 times, and there is no regularity in the magnitude and interval of the temperature rise.

[0061] Step 3: Model the historical temperature data of each water-cooled wall measured by the monitoring and positioning sensors for slagging status, and obtain the theoretical temperature value for cleaning the water-cooled wall in each area, such as... Figure 5 As shown, historical data from the monitoring and positioning sensors for slagging status of each water-cooled wall were extracted to establish the relationship between water-cooled wall temperature and boiler load. The top 5% of water-cooled wall temperature data under each load were selected for modeling to obtain the relationship between the unit's power generation load and the calculated value of water-cooled wall temperature during water-cooled wall cleaning.

[0062] Step 4: Based on the principles of heat transfer, the radiative heat transfer inside the pulverized coal furnace is calculated. The calculation process for the wall surface temperature of the water-cooled wall 3 is as follows:

[0063] During operation, the flame temperature at the center of a coal-fired boiler can reach over 1500℃. The triatomic gases in the high-temperature flue gas exert a very strong radiative heat transfer on the membrane water-cooled walls surrounding the furnace, accounting for the majority of the heat transfer within the furnace. At this point, the convective heat transfer effect of the high-temperature flue gas on the furnace membrane water-cooled walls can be ignored. The book *Boiler Principles (Third Edition)* provides a method for calculating radiative heat transfer within a pulverized coal boiler, and the model is simplified and assumed as follows:

[0064] a. Consider the cross-section of the furnace as a one-dimensional circle with a uniform cross-sectional area;

[0065] b. The flame radiation intensity varies linearly along the radial direction of the furnace.

[0066] c. The furnace height of the pulverized coal furnace is much greater than its equivalent cross-sectional radius;

[0067] d. The medium inside the furnace is ash, and the radiation intensity is independent of the wavelength.

[0068] The radiative heat transfer equation from the flame and high-temperature flue gas to the surface of the membrane water-cooled wall can be described by the following equation:

[0069]

[0070] In the formula: σ is the blackbody radiation constant, with a value of 5.67 × 10⁻⁸ W / (m²). 2 ·K 4 A w The surface area (m) of a localized region of the furnace water-cooled wall that receives flame radiation. 2 ;X f,w T is the radiation angle coefficient of the flame on the water-cooled wall surface; f and T w These represent the average flame temperature at the center of the furnace and the surface temperature of the water-cooled wall, respectively, in K; k is the total radiation attenuation coefficient; R w ε is the equivalent radiation radius from the center flame of the furnace to the surface of the water-cooled wall, in meters; f and ε w These are the emissivity of the flame at the center of the furnace and the surface of the water-cooled wall, respectively.

[0071] When the surface of the water-cooled wall is covered with slag, the radiative heat transfer from the furnace flame to the surface of the water-cooled wall is transformed into radiative heat transfer from the flame to the slag-covered surface of the water-cooled wall. Therefore, formula (2-1) can be described as follows:

[0072]

[0073] In the formula: A sll The surface area (m) of the slag layer covering a local area of ​​the water-cooled wall that receives flame radiation. 2 ;X f,w R is the radiation angle coefficient of the flame on the surface of the slag layer covering a local area of ​​the water-cooled wall. sll T is the equivalent radiation radius from the central flame in the furnace to the slag layer covering the water-cooled wall surface, in meters. sll ε is the temperature of the slag layer covering the water-cooled wall surface, in K; sll Emissivity of the slag layer covering the surface of the water-cooled wall.

[0074] Because the metallic material of the membrane water-cooled wall has a high thermal conductivity, the temperature difference at different locations within the membrane water-cooled wall in localized areas is not significantly different from the temperature difference between the flame and the water-cooled wall. Considering the large temperature difference between the furnace flame and the water-cooled wall or slag surface, the temperature difference at different locations within the slag layer along the direction parallel to the membrane water-cooled wall is obviously much smaller than the temperature difference between the furnace flame and the water-cooled wall surface. Therefore, the lateral heat transfer within the slag layer can be approximately ignored, and the heat conduction within the slag layer can be considered as a heat conduction problem only towards the water-cooled wall surface. Thus, the heat conduction within the slag layer can be approximately described using a one-dimensional heat conduction equation.

[0075]

[0076] In the formula: A is the cross-sectional area of ​​heat conduction from the outside of the slag layer to the surface of the membrane water-cooled wall, in meters. 2 δ represents the thickness of the slag layer, in meters; R s The overall thermal resistance for slagging is expressed in W / K.

[0077] Neglecting heat transfer from the water-cooled wall to the outside of the furnace (backside), in a specific local area, the heat absorbed by the working fluid inside the water-cooled wall tubes is the total enthalpy increase of the working fluid inside the tubes:

[0078] Q conv =nqΔh(4)

[0079] In the formula: n is the number of water-cooled wall tubes uniformly arranged in a specific area; q is the mass flow rate of the working fluid in the tube, kg / s; Δh is the enthalpy increase of the working fluid at both ends of the tube, kJ / kg.

[0080] According to the law of conservation of energy, for a specific local area of ​​the water-cooled wall, the radiative heat transfer Q from the furnace flame to that specific local area is... rad The heat conduction Q of the slag formation on the surface of the water-cooled wall in this specific local area cond and the convective heat transfer Q of the working fluid flowing inside the water-cooled wall tubes conv Equal, meaning the heat transfer process includes:

[0081] Q rad =Q cond =Q conv (5)

[0082] For water-cooled walls in specific areas:

[0083] A w ≈A sll ≈A(6)

[0084] X f,w ≈X f,sll (7)

[0085] R w ≈R sll (8)

[0086] According to formulas (2) to (8), when the surface of the water-cooled wall remains clean and there is no obvious slag adhering, the surface of the water-cooled wall is only affected by the radiative heat transfer from the furnace, and its surface temperature T w It can be represented as:

[0087]

[0088] When slag adheres to the surface of the water-cooled wall, eliminate T sll Its surface temperature T w It can be represented as:

[0089]

[0090] As shown in formula (10), when slag forms on the surface of the furnace water-cooled wall, without considering significant changes in boiler operation and combustion conditions, the surface temperature of the water-cooled wall will be directly affected by the thickness of the slag layer and its thermal conductivity. As the slag layer thickness increases or the thermal conductivity decreases, the surface temperature of the water-cooled wall decreases. Therefore, obtaining the surface temperature of the water-cooled wall can quickly and accurately reflect the location and severity of slag formation on the surface of the furnace water-cooled wall.

[0091] According to formula (9), when the surface of the water-cooled wall remains clean and there is no obvious slag adhering, the surface temperature T of the water-cooled wall is... w It is only affected by radiative heat transfer in the furnace. For a specific local area, its blackbody radiation constant σ and the local surface area A receiving flame radiation are... w The radiation angle coefficient X of the flame on the water-cooled wall surface f,w 1. Total radiation attenuation coefficient k; 2. Radiation equivalent radius R from the center flame of the furnace to the surface of the water-cooled wall. w All are constants, T w Mainly affected by the average flame temperature T at the center of its furnace f Flame emissivity ε at the center of the furnace f and the surface emissivity ε of the water-cooled wall w The influence of this. When the boiler load remains stable, the combustion status of the pulverized coal gas flow in the furnace is basically stable, and the average temperature T of the flame at the center of the furnace is... f Flame emissivity ε at the center of the furnace f and the surface emissivity ε of the water-cooled wall w It is almost a constant value, while at this time the mass flow rate q of the working fluid in the pipe and its enthalpy increase Δ h There is no change, and T in formula (9) remains unchanged. w Theoretically, it should be close to a constant.

[0092] When slag forms on the surface of a water-cooled wall, the surface temperature T of the water-cooled wall decreases due to the thermal resistance generated by the attached slag layer. w Theoretically, the temperature will decrease, and it will continue to decrease as the thickness δ of the slag layer increases, until the slag covering the surface of the water-cooled wall is blown off by the high-speed steam flow after soot blowing, the surface of the water-cooled wall returns to a clean state, the thermal resistance disappears, and the surface temperature T of the water-cooled wall decreases. w Theoretically, if it rises again, it will basically return to the value of a clean, slag-free state.

[0093] Meanwhile, in reality, boiler operating parameters such as pulverizer operation mode, primary / secondary air volume, and burner tilt angle frequently change during operation, causing alterations in the flow field within the furnace. At certain specific locations, when the flow field changes, the furnace may be scoured by the air or flue gas flow, potentially causing slag adhering to its surface to be blown off, thus affecting the water-cooled wall surface temperature T. w The temperature rises. However, for this localized area, due to its spatial location, the scouring effect of the furnace air or flue gas flow is often not accidental. Therefore, slag formation and slag shedding on its surface alternate repeatedly at certain time intervals. w This will also cause frequent fluctuations in levels.

[0094] The above three situations and Figure 4 The data measured by the five sensors for monitoring and locating the slagging status of the water-cooled wall are consistent with the trend.

[0095] From formulas (9) and (10), it can be seen that the surface temperature during water-cooled wall cleaning is... With actual surface temperature T w The difference between them is:

[0096] thereby:

[0097]

[0098] The above formula yields the thermal resistance of the slag layer in each local area of ​​the water-cooled wall after removing the influence of operating data. This reflects the slag formation state of the heated surface and serves as the basis for judging the degree of slag formation on the heated surface.

[0099] Step 5, according to Figure 5 Following step (4) above, the characteristic parameters of the thermal resistance of the slag layer in each water-cooled wall region before and after soot blowing are calculated, as shown in Table 1. These parameters can be used to determine the slag condition of the corresponding local area surface of the water-cooled wall and to identify the specific location of the slag on the water-cooled wall surface. ΔR s If the surface concentration is <0.04 W / K and SD <10%, the local area can be considered to have no obvious slag buildup and be in a continuously clean state; ΔR s A value >0.04 W / K and occurring only during soot blowing (10% < SD < 40%) indicates that slag formation has occurred on the surface of this localized area and needs to be removed by soot blowing; ΔR s If the slag concentration is >0.04 W / K and occurs frequently without soot blowing (SD>40%), it can be assumed that there is slag on the surface of the local area, but it will fall off on its own during boiler operation.

[0100] Table 1

[0101]

[0102] Step 6: All water-cooled wall slagging status monitoring and positioning sensors upload data to the DCS system via the data acquisition module. Long-term historical data is then analyzed to calculate the historical minimum comprehensive thermal resistance R of the slagging layer in each water-cooled wall region. s-min As a reference value during water-cooled wall cleaning, the DCS system calculates the thermal resistance of the slag layer in each water-cooled wall area in real time, such as... Figure 6 As shown, when R s -R s-min If the slag density is <0.04 W / K and the SD after the last soot blowing is <10%, then the slag buildup in the area corresponding to this sensor is slight, and the corresponding soot blower does not need to be soot blown; when R s -R s-min If the value is >0.04W / K, and the percentage after the last soot blowing is 10% < SD < 40%, then there is slag buildup in the corresponding area of ​​this sensor, which needs to be removed by the corresponding soot blower. The corresponding soot blower will then request soot blowing. When R... s -R s-min If the value is greater than 0.04 W / K and the SD is greater than 40% after the last soot blowing, then there is slag in the area corresponding to this sensor, but it will fall off on its own during boiler operation, and the corresponding soot blower does not need to be soot blown.

[0103] Step 7: The DCS system automatically calculates the soot blowing requirements of each sensor, which can accurately locate the slag formation on the water-cooled wall; it automatically issues soot blowing commands to the soot blowers that need to perform soot blowing, thus realizing closed-loop control of soot blowing.

[0104] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for monitoring and closed-loop control of slagging on boiler water-cooled walls, characterized in that, The system used includes boiler water-cooled walls, water-cooled wall slagging status monitoring and positioning sensors, data acquisition modules, DCS systems and wall-mounted soot blowers; Based on the installation location of the wall-mounted sootblowers, the water-cooled wall is divided into multiple sootblowing zones, the same number as the number of wall-mounted sootblowers, with each sootblower as the center. Each sootblowing zone includes water-cooled wall tubes, fins between the water-cooled wall tubes, and weld scars between the water-cooled wall tubes and fins. A water-cooled wall slag condition monitoring and positioning sensor is arranged within each sootblowing zone and connected to a data acquisition module for real-time monitoring of fin temperature. The data acquisition module receives data signals from the water-cooled wall slag condition monitoring and positioning sensor and transmits them to the DCS system. The DCS system receives signals from the data acquisition module, processes the data, and performs closed-loop control of each wall-mounted sootblower. The wall-mounted sootblowers, arranged within each sootblowing zone, operate according to the control commands of the DCS system to remove slag from the corresponding sootblowing zone. The method includes the following steps: Step 1: Model the historical temperature data of each water-cooled wall measured by the monitoring and positioning sensors for slagging status of each water-cooled wall to obtain the theoretical temperature value of the water-cooled wall during cleaning in each soot blowing area. ; Step 2: Based on the principles of heat transfer, construct the measured temperature of the water-cooled wall in each soot blowing zone. Theoretical temperature value during water-cooled wall cleaning Thermal resistance of slag layer on water-cooled wall R s The relationship between the three factors was analyzed, and the minimum thermal resistance of the water-cooled wall slag layer in each soot blowing area was calculated based on historical data. R s-min ; Step 3, using the thermal resistance of the slag layer on the water-cooled wall R s This reflects the slagging status of the corresponding soot blowing areas, and establishes the criteria for judging the degree of slagging in each soot blowing area and the corresponding soot blowing strategy; specifically: The DCS system measures the thermal resistance of the slag layer on the water-cooled wall in each soot blowing zone. R s Perform real-time calculations, when R s - R s-min <0.04 W / K, and after the last soot blowing SD If the slag buildup is less than 10%, the corresponding sootblower area has only slight slag buildup, and no sootblowing is required. SD Indicates standard deviation; when R s - R s-min >0.04 W / K, and less than 10% after the last soot blowing SD If the slag content is less than 40%, then the area corresponding to this sensor has slag buildup, which needs to be removed by the corresponding wall-mounted sootblower. A sootblowing request should be issued to the corresponding sootblower. R s - R s-min >0.04 W / K, and after the last soot blowing SD If the slag content is greater than 40%, then there is slag in the soot blowing area corresponding to this sensor, but it will fall off on its own during boiler operation, and the corresponding wall-mounted soot blower does not need to be soot blown. Step 4: During boiler operation, the slagging status monitoring and positioning sensors of each water-cooled wall measure the temperature of the corresponding water-cooled wall in real time, and further calculate the thermal resistance of the slagging layer on the water-cooled wall. R s Then, based on the criteria for judging the degree of slagging in each soot blowing area, the degree of slagging in each soot blowing area during boiler operation is judged. When slag forms in a certain area of ​​the water-cooled wall and needs to be removed by the corresponding sootblower, the corresponding wall-mounted sootblower requests a sootblowing request. The DCS system then issues a sootblowing command to the corresponding wall-mounted sootblower, achieving closed-loop control while monitoring the slag formation status of the water-cooled wall.

2. The method for monitoring and closed-loop control of slagging on boiler water-cooled walls according to claim 1, characterized in that, In step 2, the relationship between the measured temperature of the water-cooled wall in each soot blowing zone, the theoretical temperature during water-cooled wall cleaning, and the thermal resistance of the slag layer on the water-cooled wall is established, specifically as follows: In the formula, R s Thermal resistance of the slag layer on the water-cooled wall; The theoretical temperature value for cleaning water-cooled walls; This refers to the measured temperature of the water-cooled wall. n The number of water-cooled wall tubes in the soot blowing area is specified, and the water-cooled wall tubes are evenly distributed. q Δ is the mass flow rate of the working fluid inside the water-cooled wall tubes, kg / s; h The enthalpy increase is the change in enthalpy of the working fluid at both ends of the water-cooled wall tube, expressed in kJ / kg.

3. The method for monitoring and closed-loop control of slagging on boiler water-cooled walls according to claim 1, characterized in that, The water-cooled wall slagging status monitoring and positioning sensor includes an armored thermocouple, an external furnace fixing base, and a thermocouple protective sleeve; The external furnace mounting base is installed on the fins between two water-cooled wall tubes in each soot blowing area. One end of the thermocouple protective sleeve is fixed to the through threaded hole provided on the external furnace mounting base. The fins are provided with thermocouple mounting holes. The measuring end of the armored thermocouple passes through the thermocouple protective sleeve and the through threaded hole of the external furnace mounting base and is installed in the thermocouple mounting hole of the fin.

4. The method for monitoring and closed-loop control of slagging on boiler water-cooled walls according to claim 3, characterized in that, The depth of the thermocouple mounting hole is 50% of the fin thickness.

5. The method for monitoring and closed-loop control of slagging on boiler water-cooled walls according to claim 3, characterized in that, The thermocouple mounting hole is located between the two water-cooled wall tubes.

6. The method for monitoring and closed-loop control of slagging on boiler water-cooled walls according to claim 3, characterized in that, The radius of the arc surface on both sides of the external furnace fixing base is the same as the radius of the outer wall surface of the water-cooled wall tube. The arc surface fits tightly with the water-cooled wall tube. After fitting, there is a gap between the external furnace fixing base and the fin. The external furnace fixing base is welded to the fin by two connecting blocks.

7. The method for monitoring and closed-loop control of slagging on boiler water-cooled walls according to claim 3, characterized in that, The thermocouple protection sleeve has external threads and internal threads at both ends. The external thread at one end is connected to the furnace external fixed base, and the internal thread at the other end is connected to the fastening sleeve. The fastening sleeve has internal threads and connects to the thermocouple protective sleeve to fix the armored thermocouple.

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