An online monitoring device and method for the thickness of ash accumulation at the bottom of a horizontal flue

Abstract

The present invention provides an online monitoring device and method for the dust accumulation thickness at the bottom of a horizontal flue, comprising a measuring plate and a reference plate with the same size and heating power, which are respectively installed horizontally at the centroid of the lower wall and the upper wall of the horizontal flue; the measuring plate includes a measuring plate temperature sensor, a measuring plate heater, a measuring plate heat insulation board, a measuring plate compensation heater and a measuring plate compensation temperature sensor from top to bottom; the reference plate includes a reference plate temperature sensor, a reference plate heater, a reference plate heat insulation board, a reference plate compensation heater and a reference plate compensation temperature sensor from bottom to top; each temperature sensor is connected to a signal acquisition controller. The system structure of the present invention is simple, the algorithm is simple, and the measurement result can intuitively reflect the dust accumulation thickness at the bottom of the channel. The method based on the temperature difference of the measuring plate eliminates the influence of environmental conditions and airflow temperature, and because the temperature data within a time window is used, the influence caused by random temperature measurement errors is avoided, and the data is more stable and reliable.

Description

Technical Field

[0001] The present invention is a method and device for online monitoring of the thickness of ash deposited on the bottom of the horizontal flue of a coal-fired boiler and on the surface of the catalyst of a denitrification device, and is related to the safe, low-resistance and efficient operation of the smoke exhaust system of a coal-fired power plant. The method is also suitable for online monitoring of the deposition thickness of other solid particles at the bottom of a horizontal channel. Background Art

[0002] After coal is burned in the boiler, a large amount of solid particles will be produced. If these particles are not handled, they will cause rapid wear of the induced draft fan, and will cause environmental pollution when discharged into the atmosphere. Therefore, various dust removal measures are taken in the flue gas channel of the boiler, such as cyclone dust removal, electrostatic dust removal or bag dust removal. After dust removal, the exhaust gas of the boiler generally passes through a horizontal flue to enter the induced draft fan, and then is discharged into the atmosphere through the chimney. Since the air flow velocity in the horizontal flue is not high, the residual particles after dust removal will be deposited at the bottom of the horizontal flue under the action of gravity. This phenomenon is called ash accumulation. When the amount of ash accumulation is large, on the one hand, it will reduce the flow area of ​​the flue gas and increase the resistance of the induced draft fan. On the other hand, ash accumulation will worsen the stress state of the horizontal flue bracket and cause collapse accidents. Therefore, in consideration of economy and safe production, it is necessary to monitor the ash accumulation thickness of the horizontal flue online. In addition, in recent years, coal-fired power plants have adopted a large number of denitrification reactors to control nitrogen oxide emissions. Since ash accumulation affects the contact efficiency between the catalyst and the flue gas, it is also necessary to monitor the thickness of the ash accumulation online to determine the soot blowing cycle based on the ash accumulation thickness.

[0003] There are several online monitoring methods for the thickness of horizontal flue ash, direct methods include laser ranging, ultrasonic ranging, etc., indirect methods include airflow pressure difference monitoring and wall stress (strain) monitoring, etc. Among them, the laser ranging method fails due to pollution caused by the transmitting and receiving devices in long-term operation, the ultrasonic ranging method is limited by resolution, and environmental interference factors are difficult to eliminate, and there are too many factors affecting the airflow pressure difference and wall stress (strain) signals, which cannot meet the needs of online monitoring.

[0004] Currently, there is no recognized mature method and device for online monitoring of dust accumulation thickness in horizontal channels. Summary of the invention

[0005] Technical problem: The purpose of the present invention is to provide a method and device for online monitoring of the ash thickness of the horizontal flue according to the temperature rise signal generated by heating excitation.

[0006] Technical solution:

[0007] An online monitoring device for the ash accumulation thickness at the bottom of a horizontal flue comprises a measuring piece and a reference piece with the same size and heating power, which are respectively horizontally installed at the centroids of the lower wall and the upper wall of the horizontal flue; the measuring piece comprises, from top to bottom, a measuring piece temperature sensor, a measuring piece heater, a measuring piece heat insulation board, a measuring piece compensation heater and a measuring piece compensation temperature sensor; the reference piece comprises, from bottom to top, a reference piece temperature sensor, a reference piece heater, a reference piece heat insulation board, a reference piece compensation heater and a reference piece compensation temperature sensor; the measuring piece temperature sensor, the measuring piece compensation temperature sensor, the reference piece temperature sensor and the reference piece compensation temperature sensor are all connected to a signal acquisition controller.

[0008] Furthermore, the temperature sensor is a thin film temperature sensor with a thickness of micrometers.

[0009] Furthermore, the measuring plate heater and the reference plate heater are connected in series or in parallel and powered by the same power supply. In the loop formed, the loop current I is measured by a current sensor, and the voltage V across the heater is measured by a voltage sensor.

[0010] Furthermore, the measuring piece compensation heater and the reference piece compensation heater are powered by different power supplies, and a measuring piece power adjuster and a compensation piece power adjuster are respectively added to the two heating circuits to adjust the power of the measuring piece compensation heater and the reference piece compensation heater.

[0011] Furthermore, the measuring piece power adjuster and the compensation piece power adjuster are respectively connected to a signal acquisition controller, which controls the measuring piece power adjuster according to the temperature difference of the temperature sensors on both sides of the measuring piece, and controls the compensation piece power adjuster according to the temperature difference of the temperature sensors on both sides of the reference piece, so that the temperature difference on both sides is zero, to ensure that the heat of the heaters on both sides of the measuring piece insulation board and the reference piece insulation board is completely dissipated in the horizontal flue being measured.

[0012] An online monitoring method for the ash accumulation thickness at the bottom of a horizontal flue based on the above-mentioned online detection device comprises the following steps:

[0013] 1) After the device is powered on, first set the sampling interval Δτ and the measurement time window length τ L , calculate the number of data points in the window N = τ L / Δτ+1; input the area A or diameter D of the measuring piece and the reference piece, the thermal conductivity λ of the ash, and the PID parameters of the temperature control, and download them to the signal acquisition controller;

[0014] 2) After the measuring piece and the reference piece reach thermal stability, the signal acquisition controller records the instantaneous current I i , voltage V i , calculate the instantaneous power P i =Vi I i and the heat flux q of the measuring plate heater and the reference plate heater i =P i / 2A=V i I i / 2A; record the temperature of the measuring piece temperature sensor and the reference piece temperature sensor t mi and t ri , and calculate the temperature difference Δt i =t mi -t ri ;

[0015] 3) When the recorded data fills a time window, calculate the average heat flux density in the time window and mean temperature difference And calculate the dust thickness according to the measurement principle

[0016] 4) Shift the data by a time interval, discard the first data, add the latest measurement data to the data queue, repeat steps 2)-4), and the online continuous monitoring of dust accumulation thickness can be realized.

[0017] Beneficial effects: The present invention proposes an online monitoring device and method for the ash thickness at the bottom of a horizontal flue. The system structure is simple, the algorithm is simple, and the measurement result can intuitively reflect the ash thickness at the bottom of the channel. The method based on the temperature difference of the measuring piece eliminates the influence of environmental conditions and airflow temperature, and because the temperature data within a time window is used, the influence caused by random errors in temperature measurement is avoided, and the data is more stable and reliable. The device has low manufacturing cost, and the hardware used is common devices on the market and is very easy to obtain. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the device principle of the present invention.

[0019] Figure 2 It is a schematic diagram of the circuit structure of the present invention.

[0020] Figure 3 (a) and (b) are schematic diagrams of the structures of the measuring sheet and the reference sheet respectively used in the present invention.

[0021] Numbers in the figure: 1. Lower wall of channel; 2. Upper wall of channel; 3. Left side of channel; 4. Right side of channel; 5. Measuring piece; 6. Reference piece; 5-1. Measuring piece temperature sensor; 5-2. Measuring piece heater; 5-3. Measuring piece compensation temperature sensor; 5-4. Measuring piece compensation heater; 5-5. Measuring piece insulation board; 6-1. Reference piece temperature sensor; 6-2. Reference piece heater; 6-3. Reference piece compensation temperature sensor; 6-4. Reference piece compensation heater; 6-5. Reference piece insulation board; 7. Measuring piece and reference piece power supply; 8. Current sensor; 9. Voltage sensor; 10. Measuring piece compensation power supply; 11. Reference piece compensation power supply; 12. Measuring piece compensation power regulator; 13. Reference piece compensation power regulator; 14. Signal acquisition controller; 15. Human-machine interface. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] A constant-power electric heating measuring plate with a surface temperature sensor is installed flush with the bottom surface at the centroid of the bottom surface of the straight horizontal flue. A reference plate with the same size, heating power and surface temperature sensor as the bottom measuring plate is installed at the centroid of the upper wall surface corresponding to the bottom surface. Since the two heating plates have the same power and the same heat dissipation conditions, when there is no dust accumulation at the bottom, the temperature of the measuring plate and the reference plate should remain consistent and change synchronously with the airflow conditions in the flue and the external heat dissipation conditions. When dust accumulates at the bottom of the channel, the heat dissipation conditions on the measuring plate deteriorate. Under the condition of keeping the heating power constant, the surface temperature of the measuring plate will rise, while dust will not accumulate on the reference plate on the upper wall, so there will be no temperature change due to dust accumulation. According to the theory of heat conduction, when there is no dust accumulation on the bottom surface, the temperatures of the measuring plate and the reference plate are both Where q is the heat flux density of the measuring piece and the reference piece, which always remains unchanged; t f is the average temperature of the airflow, and h is the surface heat transfer coefficient between the airflow and the measuring and reference pieces. When dust accumulates at the bottom, the temperature of the reference piece remains unchanged, while the temperature of the measuring piece becomes Where δ is the thickness of the ash deposits and λ is the thermal conductivity of the ash. At this time, the temperature difference between the measuring piece and the reference piece is When the heating heat flux density q and the thermal conductivity λ of the ash are known, the thickness of the ash deposit can be calculated. When the thermal conductivity λ of the ash cannot be accurately predicted, the thermal resistance Indirectly characterize the dust accumulation thickness. This method of measuring the temperature difference between the measuring piece and the reference piece can eliminate the influence of air flow temperature changes and environmental conditions changes to the greatest extent.

[0024] The present invention discloses an online monitoring method and device for the thickness of dust accumulation at the bottom of a horizontal channel. The method selects a certain section of the horizontal channel (flue) to be monitored. Figure 1 . This section of horizontal channel consists of the lower wall 1, the upper wall 2, the left side 3 and the right side 4. A constant power electric heating measuring piece 5 with a surface temperature sensor is installed flush with the bottom surface at the inner center point m below the channel. The corresponding center point of the upper wall is used as the reference point r, and a reference piece 6 with the same size and heating power as the bottom measuring piece is installed. In order to reduce lateral heat loss, the measuring piece, the reference piece and the temperature sensor installed thereon are made into a film with a thickness of microns. In order to keep the heating power of the measuring piece and the reference piece to the inside of the channel constant, both of them adopt a protective heating structure, see Figure 3 .

[0025] The upper surface of the measuring piece is formed by the superposition of the measuring piece temperature sensor 5-1 and the measuring piece heater 5-2; similar to the upper surface, the lower surface is formed by the superposition of the compensation temperature sensor 5-3 and the compensation heater 5-4; the two are closely attached to the two sides of the measuring piece insulation board 5-5. The lower surface of the reference piece is formed by the superposition of the reference piece temperature sensor 6-1 and the reference piece heater 6-2; similar to the lower surface, the upper surface is formed by the superposition of the compensation temperature sensor 6-3 and the compensation heater 6-4; the two are closely attached to the two sides of the reference piece insulation board 6-5.

[0026] The measuring piece heater 5-2 and the reference piece heater 6-2 can be connected in series or in parallel and powered by the same power supply 7. The loop current I is measured by the current sensor 8, and the voltage V across the heater is measured by the voltage sensor 9. The measuring piece and reference piece compensation heaters are powered by the measuring piece compensation power supply 10 and the reference piece compensation power supply 11, respectively. The measuring piece power regulator 12 and the compensation piece power regulator 13 are added to the two heating circuits, respectively, to adjust the power of the measuring piece compensation heater and the reference piece compensation heater. The signals of the current sensor 8, the voltage sensor 9, the measuring temperature sensor 5-1 of the measuring piece, the compensating temperature sensor 5-3 of the measuring piece, the measuring temperature sensor 6-1 of the reference piece, and the compensating temperature sensor 6-3 of the reference piece are all collected and processed by the signal acquisition controller 14; the signal acquisition controller 14 also controls the measuring piece power regulator 12 according to the temperature difference between the temperature sensors 5-1 and 5-3 on both sides of the measuring piece, and controls the compensating piece power regulator 13 according to the temperature difference between the temperature sensors 6-1 and 6-3 on both sides of the reference piece, so that the temperature difference on both sides is zero, so as to ensure that all the heat of the heater is dissipated in the measured channel. The human-machine interface 15 is linked to the signal acquisition controller and is used to display and save the measurement data and calculation results.

[0027] The method for online monitoring of the ash accumulation thickness at the bottom of a horizontal flue according to the present invention is implemented on the above-mentioned device and comprises the following steps:

[0028] 1) After power on, set the sampling interval Δτ and the measurement time window length τ through the human-machine interface L, calculate the number of data points in the window N = τ L / Δτ+1; input the area A (or diameter D) of the measuring piece (reference piece), the thermal conductivity λ of the ash, and the PID parameters of the temperature control, and download them to the data acquisition controller 14;

[0029] 2) After the measuring piece and the reference piece reach thermal stability, the data acquisition controller 14 records the instantaneous current I i , voltage V i , calculate the instantaneous power P i =V i I i and the heat flux q of the measuring plate heater 5-2 and the reference plate heater 6-2 i =P i / 2A=V i I i / 2A; record the temperature t of the measuring piece temperature sensor 5-1 and the reference piece temperature sensor 6-1 mi and t ri , and calculate the temperature difference Δt i =t mi -t ri ;

[0030] 3) When the recorded data fills a time window, calculate the average heat flux density in the time window and mean temperature difference And calculate the dust thickness according to the measurement principle

[0031] 4) Shift the data by a time interval, discard the first data, add the latest measurement data to the data queue, repeat steps 2)-4), and the online continuous monitoring of dust accumulation thickness can be realized.

Claims

1. An online monitoring device for the ash accumulation thickness at the bottom of a horizontal flue, characterized in that: It comprises a measuring piece and a reference piece with the same size and heating power, which are respectively installed horizontally at the centroid of the lower wall and the upper wall of the horizontal flue; the measuring piece comprises a measuring piece temperature sensor, a measuring piece heater, a measuring piece heat insulation board, a measuring piece compensation heater and a measuring piece compensation temperature sensor from top to bottom; the reference piece comprises a reference piece temperature sensor, a reference piece heater, a reference piece heat insulation board, a reference piece compensation heater and a reference piece compensation temperature sensor from bottom to top; the measuring piece temperature sensor, the measuring piece compensation temperature sensor, the reference piece temperature sensor and the reference piece compensation temperature sensor are all connected to a signal acquisition controller; The online monitoring method based on the online detection device comprises the following steps: 1) After the device is powered on, first set the sampling interval Δτ and the measurement time window length τ L , calculate the number of data points in the window N = τ L Δτ+1; input the area A or diameter D of the measuring piece and the reference piece, the thermal conductivity λ of the ash, and the PID parameters of the temperature control, and download them to the signal acquisition controller; 2) After the measuring piece and the reference piece reach thermal stability, the signal acquisition controller records the instantaneous current I i , voltage V i , calculate the instantaneous power P i =V i I i and the heat flux q of the measuring plate heater and the reference plate heater i =P i / 2A=V i I i / 2A; record the temperature of the measuring piece temperature sensor and the reference piece temperature sensor t mi and t ri , and calculate the temperature difference Δt i =t mi -t ri ; 3) When the recorded data fills a time window, calculate the average heat flux density in the time window and mean temperature difference And calculate the dust thickness according to the measurement principle 4) Shift the data by a time interval, discard the first data, add the latest measurement data to the data queue, repeat steps 2)-4), and the online continuous monitoring of dust accumulation thickness can be realized.

2. The online monitoring device for the ash accumulation thickness at the bottom of a horizontal flue according to claim 1 is characterized in that: The temperature sensor is a thin film temperature sensor with a thickness of micrometers.

3. The online monitoring device for the ash accumulation thickness at the bottom of a horizontal flue according to claim 1 is characterized in that: The measuring plate heater and the reference plate heater are connected in series or in parallel and powered by the same power supply. In the loop formed, the loop current I is measured by a current sensor, and the voltage V across the heater is measured by a voltage sensor.

4. The online monitoring device for the ash accumulation thickness at the bottom of a horizontal flue according to claim 1 is characterized in that: The measuring piece compensation heater and the reference piece compensation heater are powered by different power supplies respectively. A measuring piece power adjuster and a compensation piece power adjuster are respectively added to the two heating circuits to adjust the power of the measuring piece compensation heater and the reference piece compensation heater.

5. The online monitoring device for the ash accumulation thickness at the bottom of a horizontal flue according to claim 4 is characterized in that: The measuring piece power adjuster and the compensating piece power adjuster are respectively connected to a signal acquisition controller, which controls the measuring piece power adjuster according to the temperature difference of the temperature sensors on both sides of the measuring piece and controls the compensating piece power adjuster according to the temperature difference of the temperature sensors on both sides of the reference piece, so that the temperature difference on both sides is zero, so as to ensure that the heat of the heaters on both sides of the measuring piece insulation board and the reference piece insulation board is completely dissipated in the horizontal flue being measured.

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