Invasive capacitive sensor, ash falling state monitoring device and monitoring method

Abstract

The invention discloses an intrusive capacitive sensor and a dust falling state monitoring device and method. The intrusive capacitive sensor comprises an instrument shell, an excitation electrode and two detection electrodes, and the excitation electrode and the two detection electrodes extend out of the instrument shell in an insulated mode; the excitation electrode and the detection electrode are flat-plate-shaped electrodes; the two detection electrodes are arranged up and down within the height range of the excitation electrode, are both parallel to the excitation electrode and have the same distance with the excitation electrode. The intrusive capacitive sensor provided by the invention can monitor the ash falling state, the ash particle speed, the concentration and other parameters in real time. The problems that in an existing ash falling monitoring method, a sensor is difficult to install and maintain, poor in anti-interference performance, uneven in sensitivity distribution and the like are solved, the method has the advantages of being easy and convenient to install and maintain, high in sensitivity, even in distribution and the like, and the requirement for monitoring the ash falling state can be better met.

Description

Technical Field

[0001] The present invention relates to the technical field of dust accumulation state monitoring, and specifically to a dust accumulation state monitoring method based on an intrusive capacitance sensor. Background Technique

[0002] Dust accumulation state monitoring refers to the technical measures taken to monitor parameters such as the falling condition, speed, and concentration of coal ash during the ash falling process in the ash hopper and silo during the ash transportation process of electrostatic precipitators. Currently, several technical means are commonly used in coal-fired power plants to monitor the dust accumulation state in the ash hopper, including microwave sensor technology, temperature sensor technology, and electrical sensor technology.

[0003] Microwave sensor technology is usually installed on the outer wall of the ash hopper. By receiving the microwave signal of the coal ash, the material level height in the ash hopper is judged, and then the dust accumulation monitoring is realized. However, microwave sensors have disadvantages such as high cost and poor anti-interference ability. Temperature sensor technology is generally installed at the connecting pipe between the ash hopper and the silo. By judging the temperature change at the pipe, the dust accumulation monitoring is realized. However, temperature sensors have disadvantages such as slow response speed and low accuracy during the monitoring process. Electrical sensor technology is mainly divided into electrostatic sensors and capacitance sensors. Due to their advantages such as simple structure, wide application range, and fast response speed, they have a relatively broad application prospect in actual industrial applications. Electrostatic sensors are passive measurement devices developed based on the particle charging phenomenon. Particles will carry a certain charge due to collisions, friction, etc. during the flowing process. The electrostatic signals carried by the particles can be collected through specific sensors and measurement circuits. Further combined with the cross-correlation algorithm, the particle speed measurement can be realized. Capacitance sensors can obtain particle concentration information by detecting the change in the equivalent dielectric constant in the measurement area between the electrode plates.

[0004] The ash falling process in the ash hopper is essentially a gas-solid two-phase flow. During actual monitoring, the circular capacitance sensor has a large diameter and is easily limited by the on-site working conditions, and there are problems such as difficult installation and maintenance, poor anti-interference ability, and uneven sensitivity distribution. Summary of the Invention

[0005] The purpose of the present invention is to provide an intrusive capacitance sensor, a dust accumulation state monitoring device, and a dust accumulation state monitoring method that are convenient for installation, anti-interference, and have high and uniform sensitivity.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] The present invention first provides an intrusive capacitive sensor, which includes an instrument housing, an excitation electrode, and two detection electrodes. One of the excitation electrodes and the two detection electrodes extend out of the instrument housing in an insulated manner; both the excitation electrode and the detection electrodes are flat plate electrodes; the two detection electrodes are arranged vertically within the height range of the excitation electrode, and both the two detection electrodes are parallel to the excitation electrode and at the same distance from the excitation electrode.

[0008] An insulating sleeve is arranged inside the instrument housing, and both the excitation electrode and the detection electrodes are arranged inside the insulating sleeve.

[0009] The instrument housing has an inner arc-shaped surface, and one of the excitation electrode and the two detection electrodes extend out of the inner arc-shaped surface of the instrument housing in an insulated manner.

[0010] Both the excitation electrode and the detection electrodes are rectangular flat plate electrodes; the two detection electrodes have the same size.

[0011] The present invention also provides a dust deposition state monitoring device, which includes:

[0012] An intrusive capacitive sensor;

[0013] A signal generator, connected to the excitation electrode of the intrusive capacitive sensor, for generating an excitation signal;

[0014] A signal detection circuit, connected to the detection electrodes of the intrusive capacitive sensor, for acquiring the capacitance signal between the detection electrodes and the excitation electrode; and obtaining the particle concentration and particle velocity according to the acquired capacitance signal.

[0015] The present invention also provides a dust deposition state monitoring method based on an intrusive capacitive sensor. By setting one capacitance sensor excitation electrode and two detection electrodes, parameters such as the velocity and concentration of ash particles during the dust deposition process are obtained using the capacitance measurement value between the excitation electrode and the detection electrodes, thereby realizing the monitoring of the dust deposition state. And by flattening the design of the electrodes and installing them in an intrusive manner, the measurement accuracy is improved and the wear is reduced, so as to solve the problems such as difficult installation and maintenance, poor anti-interference ability, and uneven sensitivity distribution existing in the prior art.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. The intrusive capacitive sensor provided by the present invention can monitor the dust deposition state, the velocity and concentration of ash particles in real time. It solves the problems such as difficult installation and maintenance, poor anti-interference ability, and uneven sensitivity distribution of the sensor in the existing dust deposition monitoring methods, and has the advantages of simpler installation and maintenance, higher sensitivity and more uniform distribution, and can better meet the needs of dust deposition state monitoring.

[0018] 2. The invasive capacitance sensor provided by the present invention adopts a flat electrode, which has higher capacitance sensitivity and better distribution uniformity compared with the existing industrial circular capacitance sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Structural diagram of the invasive capacitance sensor;

[0020] Figure 2 is Figure 1 the top view of;

[0021] Figure 3 is Figure 1 the front view of;

[0022] Figure 4 Signal detection circuit structure;

[0023] Figure 5 Capacitance sensitivity distribution of the invasive sensor of the present invention;

[0024] Figure 6 is the capacitance sensitivity distribution of the existing circular sensor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The structure of the invasive capacitance sensor provided by the present invention is as Figures 1 - 3 shown, including an excitation electrode 1, a detection electrode 2, an instrument housing 3 and an insulating sleeve 4. Among them, there are 2 detection electrodes 2. The excitation electrode 1 and the detection electrode 2 are both flat electrodes to reduce the influence on the particle movement process. The 2 detection electrodes 2 are arranged vertically, and both the 2 detection electrodes 2 are parallel to the excitation electrode 1 and at the same distance from the excitation electrode 1. The excitation electrode 1, the detection electrode 2 and the instrument housing 3 are all made of 304 stainless steel material, and the space between the excitation electrode 1 and the detection electrode 2 and the instrument housing 3 is filled and isolated by an insulating sleeve 4 made of polytetrafluoroethylene material.

[0026] For the convenience of subsequent research, the specific structural parameters of the sensor are as follows, see Figure 2 and Figure 3 : W1 = 27mm, W2 = 10mm, L1 = 5mm, L2 = 45mm, L3 = 50mm, L4 = 20mm. Among them, L1 is the electrode thickness, which is related to the sensor sensitivity. A thicker width has higher sensitivity, but it will affect the particle movement process.

[0027] The signal detection circuit of the sensor of the present invention is as Figure 4 shown. The signal generator is connected to the excitation electrode. The signal generator applies a sinusoidal excitation signal with a frequency of 500 kHz for capacitance measurement. The detection electrode is then connected to an I / V conversion circuit to realize the conversion of capacitance from a physical quantity to an electrical signal. After the conversion circuit, a null signal V is further introduced by an amplitude converter C0, the amplitude calculation of the signal is realized to obtain V C1 . Then, a differential amplifier is used to amplify the signal to obtain the final voltage signal V C2 . Therefore, a capacitance signal can be obtained from each detection electrode.

[0028] Velocity measurement method

[0029] The capacitance sensitivity distributions of the two detection electrodes of the sensor are highly similar. Therefore, when particles flow through the sensor, the capacitance signals obtained by the two detection electrodes are similar in waveform changes, but there is only a time difference. Since the center distance between the two detection electrodes is a fixed value, cross-correlation analysis can be performed on the two final voltage signals obtained by amplification and calculation from the two detection electrodes, so as to calculate the particle flow velocity. The two voltage signals are respectively denoted as V a and V b :

[0030] The expression of cross-correlation analysis can be expressed as:

[0031]

[0032] In the formula, R(n) is the cross-correlation function, N is the number of sampling points, V a (i) and V b (i) are the voltage signals measured at the i-th sampling points of the two detection electrodes of the sensor respectively, and are the average values of the signals V a and V b . The abscissa corresponding to the maximum value of the cross-correlation function is the number of offset points n0 between the two signals, and the ordinate is the cross-correlation coefficient of the two signals.

[0033] Under the condition that the signal sampling frequency f is determined, the transit time τ m can be obtained from the following formula:

[0034]

[0035] According to the distance between the two detection electrodes, the particle velocity v can be calculated:

[0036]

[0037] Among them, L is the distance between the centers of the two detection electrodes, and L = W2 + L4.

[0038] Concentration measurement method

[0039] Within the sensor measurement area, when the dielectric constant of the medium is a fixed value, within a certain concentration range, the capacitance value measured by the detection electrode has a linear relationship with the medium concentration. Therefore, for particles with a certain dielectric constant, it is necessary to calibrate the concentration before measurement. The capacitance change ΔC caused by the particle concentration β x will be converted into a voltage signal Vc through the capacitance detection circuit. Then, the functional relationship between the calibrated particle concentration β and Vc can be expressed as:

[0040] p = f(Vc)

[0041] where f(Vc) is the relationship between the measured voltage signal and the particle concentration.

[0042] By obtaining the measurement points of the empty tube and the full tube (V Ca , β a ) and (V cb , β b ) respectively under two working conditions of leaving the sensor empty and filling the sensor measurement area with particles, and fitting these two measurement points, the functional relationship between the voltage signal and the coal ash concentration can be obtained. In the sensor provided by the present invention, the measurement accuracy is improved by calculating the average value of the voltage measurement signals of the two detection electrodes.

[0043] Capacitance sensitivity verification

[0044] The capacitance sensitivity can be defined as:

[0045]

[0046] where C0 is the capacitance value when no object is inserted between the two plates of the sensor; C x is the capacitance value when an object is inserted between the two plates of the sensor; β is the volume concentration occupied by the object between the two plates of the sensor.

[0047] For the capacitance sensitivity of the sensor provided by the present invention, a sensor model is established using finite element simulation software, and an experiment is carried out by simulating the coal ash falling condition. During the simulation process, the sensor is installed in a circular ring-shaped pipeline, and coal ash particles with a particle size of 2 mm flow down from a height of 1 m from the center of the sensor and pass through the sensor detection area. The horizontal position is continuously changed at the same height for multiple ash falling simulations to calculate the capacitance sensitivity at different points of the sensor, where the β value is 1.6%.

[0048] Figure 5 is the capacitance sensitivity distribution of the sensor provided by the present invention. It can be seen that the sensitivity at different positions within the sensor measurement area is not less than 1.8, and the maximum difference is 0.075.

[0049] The capacitance sensitivity distribution of a typical circular ring-shaped sensor under the same working conditions, such as Figure 4As shown in the figure. Among them, the inner diameter of the sensor is 45 mm. From Figure 6 it can be seen that the sensitivity of the circular ring capacitive sensor is the highest in the central region, not higher than 1.2 at most, and the sensitivity in the edge region is relatively low, only about 0.2 at most. Due to factors such as temperature drift and harsh on-site working conditions, the sensitivity of the circular ring capacitive sensor can only be further increased to about 1.5 through methods such as self-calibration structure, differential electrodes, and anti-vibration design, and there is still a problem of uneven sensitivity distribution. In contrast, the central sensitivity of the sensor provided by the present invention is about 0.6 higher than that of the circular ring sensor, and the edge sensitivity is about 1.6 higher, and the sensitivity uniformity in the measurement area is better.

Claims

1. An intrusive capacitive sensor, comprising an instrument housing, an excitation electrode and two detection electrodes, characterized in that: One of the excitation electrodes and two of the detection electrodes extend out of the instrument housing in an insulated manner; both the excitation electrode and the detection electrodes are flat electrodes; the two detection electrodes are arranged vertically within the height range of the excitation electrode, and both the two detection electrodes are parallel to the excitation electrode and at the same distance from the excitation electrode.

2. The invasive capacitance sensor according to claim 1, wherein An insulating sleeve is provided within the instrument housing, and both the excitation electrode and the detection electrodes are arranged within the insulating sleeve.

3. The invasive capacitance sensor according to claim 1, characterized in that The instrument housing has an inner arc-shaped surface, and one of the excitation electrodes and two of the detection electrodes extend out of the inner arc-shaped surface of the instrument housing in an insulated manner.

4. The invasive capacitance sensor according to claim 3, wherein The diameter of the inner arc-shaped surface of the instrument housing is the same as the diameter of the pipeline to be measured.

5. The invasive capacitance sensor according to claim 4, characterized in that, Both the excitation electrode and the detection electrodes are rectangular flat electrodes.

6. The invasive capacitance sensor according to claim 5, characterized in that, The two detection electrodes have the same size.

7. A dust accumulation state monitoring device, characterized in that, Comprising: The invasive capacitance sensor according to any one of claims 1-6; A signal generator, connected to the excitation electrode of the invasive capacitance sensor, for generating an excitation signal; A signal detection circuit, connected to the detection electrodes of the invasive capacitance sensor, for acquiring the capacitance signal between the detection electrodes and the excitation electrode; and obtaining the particle concentration and particle velocity according to the acquired capacitance signal.

8. The dust accumulation state monitoring device according to claim 7, wherein The signal detection circuit performs a cross-correlation calculation on the two capacitance signals obtained from the two detection electrodes to obtain the particle flow velocity; the signal detection circuit converts the acquired capacitance signal into a voltage signal, and obtains the particle concentration through the calibrated functional relationship between the particle concentration and the voltage signal.

9. A method for monitoring the dust deposition state, which is detected by using the dust deposition state monitoring device according to claim 7, is characterized in that Comprising: Install the invasive capacitance sensor according to any one of claims 1-6 on the coal ash pipeline; Generate an excitation signal on the excitation electrode of the invasive capacitance sensor through the signal generator; Obtain the capacitance signal between the detection electrodes and the excitation electrode of the invasive capacitance sensor in real time; Monitor the ash falling state according to the capacitance signal between the detection electrode and the excitation electrode obtained in real time.

10. A method for monitoring the ash accumulation state according to claim 9, characterized in that, The ash falling state monitoring includes ash falling speed monitoring and ash falling concentration monitoring.

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