CN212808613U - Concentration and speed detection device for gas-solid two-phase flow - Google Patents
Concentration and speed detection device for gas-solid two-phase flow Download PDFInfo
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- CN212808613U CN212808613U CN202021337314.8U CN202021337314U CN212808613U CN 212808613 U CN212808613 U CN 212808613U CN 202021337314 U CN202021337314 U CN 202021337314U CN 212808613 U CN212808613 U CN 212808613U
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Abstract
The invention provides a device for detecting the concentration and the speed of a gas-solid two-phase flow, which integrates a microwave radar sensor and 2 arc electrodes on a shielding cover, adopts the microwave radar sensor to measure the concentration of powder and adopts a cross-correlation electrostatic method to measure the speed of the powder, realizes the real-time measurement of the concentration and the speed of the powder conveyed at the same position of a conveying pipeline, thereby obtaining more accurate mass flow of the powder, providing real-time data for the adjustment and the control of a powder conveying system, and the microwave radar sensor and the arc electrodes are all installed in a non-intrusive way, do not interfere the flow of the powder during the detection, have no abrasion problem of the sensors, have less operation and maintenance amount, and can be widely used for the real-time monitoring of the conveying process of the gas-solid two-phase flow in the industries of electric.
Description
Technical Field
The invention belongs to the technical field of gas-solid two-phase online monitoring, and particularly relates to a device for detecting the concentration and the speed of a gas-solid two-phase flow.
Background
The pneumatic powder conveying process is a complex gas-solid two-phase flow process, and the process exists in various industrial production flows in large quantity. For example, the primary air powder feeding of coal-fired thermal power plants, the wind power pipeline conveying of cement, the pneumatic conveying of flour of food plants, the conveying of chemical material particles and the like. Two flow parameters that users are concerned about when powder is conveyed pneumatically are the concentration and speed of gas-solid two-phase flow. Taking the primary air powder feeding of a coal-fired power plant as an example, pulverized coal ground by a coal grinding machine is delivered to a combustor through a pipeline and is sprayed into a hearth for combustion, while one coal grinding machine is generally distributed to 4 or 6 primary air powder pipes at the same time, because the resistance in each pipe is different, the concentration and the speed of the pulverized coal in each powder conveying pipe are different, and the concentration and the speed deviation are more than 30% in severe cases. And the deviation of the concentration and the speed of the pulverized coal in each pulverized coal pipeline can cause the blockage and the breakage of the powder conveying pipe and the deflection of the flame at the combustion center of the boiler, thereby generating a plurality of potential safety hazards. Meanwhile, the boiler combustion efficiency is reduced due to the uneven air and powder distribution of each powder pipe, and the NOx emission is increased. Therefore, the accurate measurement of the concentration and the speed of the powder or the particles has important significance on the control of the production process, the improvement of the conveying efficiency, the guarantee of the product quality, the energy conservation and the consumption reduction as well as the flow measurement.
At present, many techniques are available for powder concentration and velocity measurement, such as laser, ultrasound, electrostatic, microwave, nuclear radiation, capacitance, etc. However, most techniques are not mature enough, or the structure is complex and the cost is expensive. The electrostatic sensor has been developed in recent years due to its advantages of relatively simple structure, relatively low cost, high sensitivity, etc.
The electrostatic sensor has two forms, namely an invasive electrode and a non-invasive ring electrode. The invasive electrode generally adopts a metal probe and is inserted into a measured pipeline, although the installation is convenient, the electrode needs to be replaced regularly due to larger abrasion. The annular electrode is an annular metal electrode with the same inner diameter as the user pipeline, the electrode is embedded in the sensor pipeline, although the problem of electrode abrasion is solved, when the conveying pipe diameter is larger (for example, the diameter of a primary air pipe of a coal-fired power plant is usually more than 400 mm), the manufacturing cost of the sensor is high, and when the sensor is additionally arranged on the existing pipeline, a section of the original powder conveying pipeline needs to be cut off, and then the pipeline sensor with the annular electrode needs to be welded, so that the field installation construction amount is large.
The principle of electrostatic powder detection is that charge signals carried by powder in a metal electrode induction pneumatic powder conveying pipe are filtered, amplified and converted, and a calibration curve is obtained by calibration by using the positive correlation between the root mean square RMS of the electrostatic induction signals and the powder concentration, so that the powder concentration is calculated.
The speed measurement is obtained by adopting a cross-correlation principle, namely, the static signals obtained by two annular static induction electrodes arranged in parallel at the upstream and the downstream (distance S) of a measured pipeline are subjected to cross-correlation coefficient peak value calculation, so that the transit time (T) of the signals of the two electrostatic electrodes at the upstream and the downstream is obtained, the transit time represents the time taken by the powder to move from the upstream to the downstream, and the powder speed can be calculated by dividing the distance (S) by the time (T).
However, in practical applications, since the diameter of the powder conveying pipe to be measured is large, and the ring-shaped electrode is mounted on the wall of the pipe, only the powder near the electrode can be effectively detected, and the electrical signal induced by most of the powder in the pipe on the ring-shaped electrode is very weak, which results in a representative error of concentration measurement. In fact, the flowing speed of the powder has a large influence on the intensity of the electrostatic signal, the higher the speed is, the higher the intensity of the electrostatic signal measured by the electrostatic sensor is, but there is no clear mathematical relationship between the speed of the powder and the intensity of the electrostatic signal, so that the measurement error caused by the speed change of the powder is difficult to eliminate; in addition, the moisture content of the powder is an important factor influencing the concentration measurement accuracy of the electrostatic sensor, and the higher the moisture content is, the smaller the electrostatic signal intensity measured by the electrostatic sensor is, so that a larger error is brought to the concentration measurement. At present, no good solution exists for the measurement error, so that the concentration signal given by the electrostatic measurement method can only be reflected as a concentration trend in most cases, and the absolute measurement error is large.
Disclosure of Invention
The invention solves the technical problem of providing a device for detecting the concentration and the speed of gas-solid two-phase flow, which adopts a microwave radar sensor to measure the concentration of powder and a cross-correlation electrostatic method to measure the speed of the powder, realizes the real-time measurement of the concentration and the speed of the conveyed powder at the same position of a conveying pipeline, thereby obtaining more accurate mass flow of the powder, providing real-time data for the adjustment and the control of a powder conveying system, and being widely used for the real-time monitoring of the conveying process of the gas-solid two-phase flow in the industries of electric power, cement, food, chemical engineering and the like.
The technical solution for realizing the purpose of the invention is as follows:
a device for detecting the concentration and the speed of gas-solid two-phase flow comprises a shielding cover, wherein the shielding cover is fixedly arranged on a conveying pipeline through a pipeline welding flange; a pair of arc electrodes which are arranged in parallel are embedded in the shielding cover, and the arc electrodes are respectively electrically insulated from the conveying pipeline through an electric insulating plate; a radar mounting tube seat is arranged on the shielding cover between the two arc electrodes in a penetrating manner, a radar probe of the microwave radar sensor is inserted into and fixed in the radar mounting tube seat, and the end face of the radar probe of the microwave radar sensor is flush with the inner wall of the conveying pipeline; the circuit mounting box is installed to surface one side of shield cover, installs electrode terminal and circuit board in the circuit mounting box, electrode terminal links to each other with the circuit board, and electrode terminal runs through circuit mounting box bottom, shield cover, electric insulation board in proper order after electrically continuous with arc electrode, and electrode terminal's surface passes through insulating material and circuit mounting box, shield cover realization electrical insulation.
Furthermore, the device for detecting the concentration and the speed of the gas-solid two-phase flow is characterized in that a shell of the circuit mounting box, an electrode binding post and an arc electrode are all made of metal materials.
Furthermore, the device for detecting the concentration and the speed of the gas-solid two-phase flow has the advantages that the length of the arc-shaped electrode is 1/10-1/2 of the perimeter of the conveying pipeline, and the width of the arc-shaped electrode is 4-40 mm.
Furthermore, the device for detecting the concentration and the speed of the gas-solid two-phase flow has the same radius of the inner arc surface of the arc electrode as the inner diameter of the conveying pipeline.
Furthermore, the device for detecting the concentration and the speed of the gas-solid two-phase flow has the same shape of the two arc-shaped electrodes, and the distance between the two arc-shaped electrodes is 5-50 cm.
Furthermore, the microwave radar sensor of the device for detecting the concentration and the speed of the gas-solid two-phase flow is a planar microstrip medium resonant Doppler radar or a waveguide resonant Doppler radar.
Furthermore, the device for detecting the concentration and the speed of the gas-solid two-phase flow has the working frequency of the microwave radar sensor being an X wave band, namely 8-12 GHz, or a K wave band, namely 18-27 GHz.
Compared with the prior art, the invention adopting the technical scheme has the following technical effects:
1. the device for detecting the concentration and the speed of the gas-solid two-phase flow simultaneously carries out online real-time measurement on the concentration and the flow speed of the powder in the gas-solid two-phase flow, and synchronously measures the concentration and the speed of the powder at the same position in a pipeline, and the acquired signal has stronger authenticity and representativeness.
2. The microwave radar sensor and the arc-shaped electrode in the device for detecting the concentration and the speed of the gas-solid two-phase flow are all installed in a non-invasive manner, so that the flow of powder is not interfered during detection, the sensor has no abrasion problem, and the operation and maintenance amount is small.
3. Compared with the annular electrode, the arc-shaped electrode structure adopted in the device for detecting the concentration and the speed of the gas-solid two-phase flow has the advantages of low manufacturing cost, convenient installation and small modification construction amount.
Drawings
FIG. 1 is a schematic view showing the structure of a device for detecting the concentration and velocity of a gas-solid two-phase flow according to the present invention.
Fig. 2 is a schematic view of fig. 1 taken along direction a.
Reference signs mean: the method comprises the following steps of 1-conveying pipeline, 2-pipeline welding flange, 3-shielding case, 4-circuit installation box, 5-electrode binding post, 6-microwave radar sensor, 7-radar probe, 8-radar installation tube seat, 9-electric insulation board, 10-arc electrode, 11-electric insulation board and 12-radar probe end face.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
Example 1
A concentration and speed detection device of gas-solid two-phase flow is convenient to install and use, a microwave radar sensor 6 and 2 arc electrodes 10 are integrated on a shielding case 3 at the same time, and the concentration and speed real-time measurement of powder conveying can be realized at the same position of a conveying pipeline 1, so that more accurate powder mass flow can be obtained.
The detection device comprises a shielding case 3, wherein the shielding case 3 is fixedly arranged on a conveying pipeline 1 through a pipeline welding flange 2.
The embedded arc electrode 10 that has a pair of parallel arrangement of shield cover 3, two arc electrodes 10's shape is the same, and the top view is rectangular shape, and the length of arc electrode 10 is 1/10 ~ 1/2 of pipeline 1 girth, and the width is 4 ~ 40mm, and distance each other is 5 ~ 50cm, and the intrados radius of arc electrode 10 is the same with the internal diameter of pipeline 1. The arc-shaped electrodes 10 are electrically insulated from the conveying pipe 1 by means of electrical insulation plates 9, respectively. The shielding case 3 between two arc electrodes 10 is provided with a radar mounting tube seat 8 in a penetrating manner, the radar probe 7 of the microwave radar sensor 6 is inserted into and fixed in the radar mounting tube seat 8, the radar probe end face 12 of the microwave radar sensor 6 is flushed with the inner wall of the conveying pipeline 1, and the microwave radar sensor 6 adopts a plane micro-strip medium resonance Doppler radar or a waveguide resonance Doppler radar. The working frequency of the microwave radar sensor 6 is X wave band, namely 8-12 GHz, or K wave band, namely 18-27 GHz. The operating frequency of the microwave radar sensor 6 is preferably 24.12Ghz, which is commonly used in the industry. The microwave radar sensor 6 is composed of circuits such as a microwave oscillation source, a power divider, a transmitting antenna, a receiving antenna, a mixer, a wave detector and the like.
Circuit mounting box 4 is installed to surface one side of shield cover 3, installs electrode terminal 5 and circuit board in the circuit mounting box 4, electrode terminal 5 links to each other with the circuit board, and electrode terminal 5 runs through in proper order 4 bottoms of circuit mounting box, shield cover 3, electric insulation board 9 back and arc electrode 10 electricity and links to each other, and electrode terminal 5's surface passes through insulating material and circuit mounting box 4, shield cover 3 realization electrical insulation.
The shell of the circuit mounting box 4, the electrode binding post 5 and the arc-shaped electrode 10 are all made of metal materials.
The device also comprises an analysis processing unit for microwave radar Doppler signals, an analysis processing unit for electrostatic electrode sensor signals, and a collection, operation, storage, display and signal transmission unit.
The device for detecting the concentration and the speed of the gas-solid two-phase flow comprises the following steps:
step 1: a microwave radar sensor is arranged on the pipeline, transmits microwave signals into the conveying pipeline through the end surface of a radar probe, and receives microwave Doppler frequency shift signals reflected by powder.
According to the Doppler effect, the microwave meets the powder flowing in the pipeline to generate a Doppler frequency shift signal, and the Doppler frequency shift signal contains the scattering intensity of the powder to the microwave, so that the Doppler frequency shift signal contains the mass or concentration information of particles. Because the microwave radiation signal basically covers most of the interior of the pipeline, the amplitude of the Doppler frequency shift signal is the result of the combined action of all powder particles directly radiated by the transmitting antenna, and therefore the detected signal is high in representativeness. Because the microwave Doppler frequency shift signal amplitude has no direct relation with the powder motion speed, temperature, pressure, electrification condition and the like, the detection precision is less influenced by the outside. The microwave Doppler frequency shift signal only has signal output to the moving powder, so that the concentration measurement of the powder deposited on the wall of the pipeline is not influenced. The calibration curve coefficient of the measured powder is obtained by calibrating microwave Doppler frequency shift power signals of the measured powder at different concentrations, so that the concentration of the powder can be calculated. The number of microwave radar sensors can be increased on the cross section of the pipeline to improve the detection accuracy.
Step 2: according to the research theory, if the powder particles are irradiated by microwaves, the wavelength of the microwaves is far larger than the diameter of the powder particles, and then the particles generate Rayleigh scattering to the microwaves. The scattering cross-sectional area of a particle in the rayleigh region is inversely proportional to the fourth power of the wavelength and proportional to the sixth power of the particle diameter. For solid spherical particles, the particle radius also reflects the particle mass, i.e. the scattering cross-sectional area is related to the particle mass. It is theorized that the mass or concentration of the particles can be obtained by measuring the scattered energy of the particles to the microwaves.
The specific method comprises the following steps: analyzing the collected microwave Doppler frequency shift signals, and calculating to obtain the concentration of the powder:
step 2-1: calculating an autocorrelation function of the doppler shifted signal:
wherein k is 0,1,2, …, N-1, N is the number of sampling data, j is a transition parameter without practical meaning, and x () is a doppler shift signal function; rxx (k) is a discrete estimate of the autocorrelation function of a finite long-time sequence.
Step 2-2: performing fast fourier transform on the autocorrelation function to obtain a power spectral density pxx (k):
wherein, pxx (k) is power spectrum estimation.
Step 2-3: and the concentration of the powder is related to the power of the Doppler echo signal, so that the frequency integration is carried out on the power spectral density to obtain the echo power P:
wherein f ismaxIs the maximum frequency, f, of the Doppler echo signalminIs the minimum frequency of the doppler echo signal. In the background of gas-solid two-phase flow, the frequency of the Doppler echo signal is actually concentrated in a certain frequency band, and can be obtained by adopting an actual measurement method. Or another method is to estimate the bandwidth of the echo signal according to the power spectral density, and the estimation method is as follows: because the solid particles do not have echoes outside the beam, the frequency of the echoes continuously changes along with the continuous change of the distance between the moment of entering the beam and the moment of leaving the beam, and the amplitude and the frequency of the echo signals have sudden changes at the two moments, the Doppler bandwidth can be estimated by utilizing the sudden changes at the two moments. A straight line is obtained by accumulating the minimum value point and the maximum value point of the integral curve in the power spectrum, the straight line is intersected with the integral curve to divide the integral curve into two sections, the distances from the points on the two sections to the straight line respectively have a maximum value, and the frequency points corresponding to the two maximum values are determined as two frequency end points of the Doppler bandwidth.
Step 2-4: the concentration of the flowing powder and the square value of the echo power are in positive correlation, the K coefficient is calculated according to the calibration curve of the specific powder, and the powder concentration c is calculated:
wherein K is obtained from the calibration curve of the powder.
And step 3: the two arc electrodes receive signals generated by the static charge of the solid particles in the conveying pipeline, and the signals are respectively as follows:
X(t)＝S(t)+k1(t)
Y(t)＝S(t-D)+k2(t)
wherein X (t), Y (t) respectively represent upstream arc electrodesSignals received by the electrode and the downstream arc electrode, S (t) is a signal source signal, namely a signal generated by electrostatic charge of solid particles, D is the time difference, namely time delay, k of the signals received by the two arc electrodes1(t) and k2(t) is the noise at the two arc-shaped electrodes. Based on the physical characteristics of the noise source, it can be assumed that kl (t), k2(t) is white gaussian noise with zero mean and generalized stationary, and is statistically independent from each other and from the source signal s (t).
And 4, step 4: performing cross-correlation processing on signals X (t) and Y (t) received by the arc motor, and calculating to obtain the speed of the powder:
step 4-1: in actual measurement, the waveforms of signals acquired by the upstream arc electrode and the downstream arc electrode are similar, and the signal on the downstream arc electrode is different from the signal on the upstream arc electrode by a time tau. Calculating the cross-correlation function of the signals x (t), y (t) according to the statistical properties of the received signals, and solving the peak of the cross-correlation function:
Rxy(t)＝E{X(t)Y(t-τ)}＝Rs(τ-D)
the above equation shows that the cross-correlation function rxy (t) of the received signals x (t) and y (t) is equal to the autocorrelation function of the source signal s (t), and reaches a maximum when t ═ D;
step 4-2: calculating a transition time value tau corresponding to the maximum value of the cross-correlation function Rxy (t), wherein tau is a time delay value D;
step 4-3: calculating the powder speed V:
V＝S/D
wherein S is the distance between the upstream and downstream arc electrodes (10).
The foregoing is directed to embodiments of the present invention and, more particularly, to a method and apparatus for controlling a power converter in a power converter, including a power converter, a power.
Claims (7)
1. The device for detecting the concentration and the speed of the gas-solid two-phase flow is characterized by comprising a shielding cover (3), wherein the shielding cover (3) is fixedly arranged on a conveying pipeline (1) through a pipeline welding flange (2);
a pair of arc electrodes (10) which are arranged in parallel are embedded in the shielding cover (3), and the arc electrodes (10) are electrically insulated from the conveying pipeline (1) through electrical insulation plates (9) respectively; a radar mounting tube seat (8) is arranged on the shielding cover (3) between the two arc-shaped electrodes (10) in a penetrating mode, a radar probe (7) of the microwave radar sensor (6) is inserted into and fixed in the radar mounting tube seat (8), and the radar probe end face (12) of the microwave radar sensor (6) is flush with the inner wall of the conveying pipeline (1);
the circuit mounting box (4) are installed to surface one side of shield cover (3), install electrode terminal (5) and circuit board in the circuit mounting box (4), electrode terminal (5) link to each other with the circuit board, and electrode terminal (5) run through in proper order behind circuit mounting box (4) bottom, shield cover (3), electrical insulation board (9) and arc electrode (10) electrical connection, and the surface of electrode terminal (5) passes through insulating material and circuit mounting box (4), shield cover (3) and realizes electrical insulation.
2. The device for detecting the concentration and the speed of a gas-solid two-phase flow according to claim 1, wherein the shell of the circuit mounting box (4), the electrode binding post (5) and the arc-shaped electrode (10) are made of metal materials.
3. The apparatus for detecting the concentration and velocity of a gas-solid two-phase flow according to claim 1, wherein the length of the arc-shaped electrode (10) is 1/10-1/2 of the perimeter of the conveying pipe (1), and the width is 4-40 mm.
4. A gas-solid two-phase flow concentration and velocity detection apparatus according to claim 1 or 3, wherein the intrados radius of the arc electrode (10) is the same as the inner diameter of the transfer pipe (1).
5. The gas-solid two-phase flow concentration and velocity detection device according to claim 1 or 3, wherein the two arc electrodes (10) are identical in shape and are spaced from each other by 5-50 cm.
6. The apparatus for detecting the concentration and velocity of a gas-solid two-phase flow according to claim 1, wherein the microwave radar sensor (6) is a planar microstrip dielectric resonant doppler radar or a waveguide resonant doppler radar.
7. The apparatus for detecting concentration and velocity of gas-solid two-phase flow according to claim 1 or 6, wherein the operating frequency of the microwave radar sensor (6) is X band, i.e. 8 to 12GHz, or K band, i.e. 18 to 27 GHz.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111781114A (en) * | 2020-07-09 | 2020-10-16 | 南京大得科技有限公司 | Device and method for detecting concentration and speed of gas-solid two-phase flow |
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