A method for measuring particle mass flow

Abstract

The present invention provides a method for measuring particle mass flow. The method discretizes the air-powder mixture passing through fixed blades into multiple particle microelements along the circumferential arrangement direction of the sensor. The microelements collide with the pipe wall during spiral motion to generate tangential force, radial force, and axial force, causing the sensor to generate a deformation output voltage. The present invention fits the relationship between the microelement mass and voltage, uses the discretization method to calculate the mass M of the coal powder, and then uses the cross-correlation method to calculate the transit time of the particles between the two layers of sensors, thereby obtaining the mass flow Q. m The present invention relies on the piezoelectric effect and the particle dynamics model to measure the mass flow of particles in the air powder, thereby ensuring the accuracy of the coal powder mass flow measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of automated detection, and in particular relates to a method for measuring particle mass flow. Background Art

[0002] Two-phase flow is a multidisciplinary, comprehensive technical science that connects several fundamental sciences with extensive engineering applications. It is widely used not only in the energy, chemical, metallurgical, building materials, and environmental sectors, but also in industries closely related to daily life, such as textiles, food, and medicine. The measurement of the mass flow rate of particles in the gas phase, the mass flow rate of liquid droplets in the gas phase, and the mass flow rate of particles in the liquid phase is widely demanded across various industries.

[0003] Gas-solid two-phase flow mass flow measurement technology has long been widely implemented in modern industrial development. Its measurement accuracy directly impacts the stability of industrial production systems and is crucial for improving production efficiency and reducing resource waste. This is particularly true in pulverized coal-fired power generation in the energy industry. Pulverized coal, ground in the pulverizer, is carried by the primary air, separated by a separator, and then enters the furnace for combustion. This is a typical gas-solid two-phase flow, and measuring the mass flow of pulverized coal is an urgent problem. Most power plants in my country use either tangential or opposed combustion. In actual operation, uneven air-to-powder concentrations between pulverized coal pipes in the same burner layer can cause flame center deviation and coking on the water-cooled wall, compromising safe boiler operation. Furthermore, uneven pulverized coal concentrations can cause blockage in the pulverized coal pipes, impacting combustion stability. Severe blockages can even lead to low-load operation or even shutdown. The mass flow rate of pulverized coal in the pipes determines its concentration. Accurate and timely knowledge of the mass flow rate of pulverized coal in the pipes improves furnace combustion stability and efficiency and provides important guidance for furnace combustion.

[0004] Existing pulverized coal mass flow measurement systems have many problems. For example, Chinese invention patent CN107764351A discloses a method for real-time online measurement of gas-solid two-phase mass flow based on an electrostatic method. The method includes the following steps: Step 1: Calculating the electrostatic signal energy function; Step 2: Calculating the mass flow scalar based on the electrostatic signal energy function obtained in Step 1; Step 3: Calibrating different mass flow rates based on the mass flow scalar obtained in Step 2; Step 4: Measuring the solid mass flow rate of the gas-solid two-phase flow. Numerous factors affect particle charge in this electrostatic measurement system, resulting in a lack of clear relationship between particle charge and mass flow rate, large deviations between measurement results and actual results, and severe equipment wear during ultrasonic measurement. The pulverized coal conveying process in pulverized coal pipelines is a complex gas-solid two-phase flow, and measuring its mass flow rate remains a challenge. Summary of the Invention

[0005] The present invention aims to provide a method for measuring particle mass flow, so as to solve the technical problem that the measurement result of the existing pulverized coal mass flow measurement system deviates too much from the actual result.

[0006] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0007] A method for measuring particle mass flow, the method comprising the following steps:

[0008] Step 1: Powder is transported from bottom to top in a pipe. A sensor and a swirl device are provided in the pipe. The sensor is mounted on the inner wall of the pipe and is located above the swirl device. Powder passing through the swirl device forms a circular particle layer on the inner wall of the pipe.

[0009] Step 2: The sensor receives the stress signal and transmits the signal to the processor, which calculates the particle mass M on each layer of the sensor on the pipe wall at this time using the following formula:

[0010]

[0011] Where: m i is the mass of a single particle element on the discretized piezoelectric film, i is the sensor number, and N is the number of sensors;

[0012] Step 3: The processor obtains the particle mass flow rate Q in the pipeline by the following calculation formula: m :

[0013] Q m =M / τ k ;

[0014] Where: τ k is the transit time of particles between two adjacent layers of sensors.

[0015] Thus, the wind and dust are transported from bottom to top in the pipeline and flow through the swirl device. Due to the structure of the swirl device, the wind and dust mixture generates a tangential velocity after passing through the fixed blades. When flowing out of the fixed blades, due to the action of centrifugal force, the particles will move to the inner wall of the pipeline and move upward in a spiral along the pipeline wall to form a circular ring-shaped particle layer with uniform concentration. The particle layer is discretized into N particle elements along the circumferential direction (N is the number of sensors). During the movement, the particle layer comes into contact with the pipeline wall. The sensor installed on the inner wall of the pipeline receives a stress signal, transmits the signal to the processor and obtains the particle mass flow rate in the pipeline. The present invention relies on the piezoelectric effect and the particle dynamics model to measure the particle mass flow rate in the wind and dust, thereby ensuring the accuracy of the coal powder mass flow rate measurement.

[0016] Furthermore, before step 2, the processor calculates the centrifugal force F exerted on the particles in the particle layer in the radial direction by the following formula: cent and drag force F DN , the drag force F on the particle in the axial direction DA , and the drag force F on the particle in the tangential direction DT :

[0017]

[0018]

[0019]

[0020]

[0021] Where: m is the mass of the particle, R is the radius of the pipe, v 切向 is the tangential velocity of the particle, ρ g is the density of the fluid, A p is the frontal area of ​​the particle in the flow field, u sN is the radial velocity difference between the particle and the fluid, C d is the drag coefficient, u sA is the axial velocity difference between particles and fluid, u sT is the tangential velocity difference between the particle and the fluid.

[0022] Furthermore, the processor calculates the force F exerted by the particles on the sensor in the tangential direction by the following formula: T The sensor is subjected to a force F exerted by particles in the radial direction. N , and the axial force F exerted on the sensor by the particles A :

[0023] F T =F DT -μF N ;

[0024] F N =F cent -F DN ;

[0025] F A =F DA -mg-μF N ;

[0026] Where: m is the mass of the particle, g is the acceleration due to gravity.

[0027] Furthermore, the processor calculates the output charge Q and the output voltage signal U using the following formula:

[0028] Q=(d31 ε1+d 32 ε2+d 33 ε3)E PVDF S;

[0029] Where: d 31 d 32 d 33 are the piezoelectric constants of the PVDF piezoelectric film in the x, z and y directions, ε1, ε2, ε3 are the strains of the PVDF piezoelectric film in the x, z and y directions, E PVDF is the elastic modulus of the sensor (2), S is the area of ​​the piezoelectric film;

[0030]

[0031] Where: C f is the feedback capacitance of the charge amplifier.

[0032] A method for measuring particle mass flow of the present invention has the following advantages:

[0033] 1) A method for measuring the mass flow rate of pulverized coal is proposed, in which the centrifugal force generated by the pipe wall after the impeller rotates is used, and the output voltage of the sensor is used to measure the mass flow rate of pulverized coal. The theoretical method is simple and verifiable, the measurement process is not affected by the type of particles, and the accuracy can be adjusted according to the arrangement of the sensor, thus overcoming the limitations of existing measurement methods.

[0034] 2) The structure is simple. It only needs to add blades in front of the measuring part to form a swirl and add a sensor to the measuring part to accurately measure the mass flow of particles.

[0035] 3) PVDF piezoelectric film sensor has the advantages of wear resistance, ductility, high piezoelectric coefficient and fast response speed, and is well suited for measuring the mass flow rate of gas-solid two-phase flow in pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of the first embodiment of the measuring system of the present invention, in which A is a longitudinal sectional view of the measuring system and B is a transverse sectional view of the measuring system;

[0037] Figure 2 Schematic diagram of the structure of a second embodiment of the measuring system of the present invention, in which A is a longitudinal sectional view of the measuring system and B is a transverse sectional view of the measuring system;

[0038] Figure 3 Schematic diagram of the structure of the third embodiment of the measuring system of the present invention, in which A is a longitudinal sectional view of the measuring system and B is a transverse sectional view of the measuring system;

[0039] Figure 4is a flow chart of a method for measuring particle mass flow rate according to the present invention;

[0040] Figure 5 This is a force analysis diagram of the particle microelement of the present invention in contact with the PVDF piezoelectric film in the tangential and radial directions;

[0041] Figure 6 This is a force analysis diagram of the particle microelement of the present invention in contact with the PVDF piezoelectric film in the axial direction;

[0042] Figure 7 This is a force analysis diagram of the particle microelement of the present invention in contact with the PVDF piezoelectric film in a vertical pipe;

[0043] Figure 8 It is a schematic diagram of the array sensors in the axial and tangential directions of the inner wall of the pipeline of the present invention.

[0044] Explanation of the markings in the figure: 1. Pipeline; 2. Sensor; 3. Particle layer; 4. Cyclone device. DETAILED DESCRIPTION

[0045] In order to better understand the purpose, structure and function of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0046] like Figure 1 and Figure 4 As shown, the main working process of a method for measuring particle mass flow in this embodiment is as follows:

[0047] The wind powder is transported from bottom to top in the pipe 1. The pipe 1 is provided with a sensor 2 and a swirl device 4. The sensor 2 is installed on the inner wall of the pipe 1 and is located above the swirl device 4. The wind powder passing through the swirl device 4 forms a circular particle layer 3 on the inner wall of the pipe 1, and the particle layer 3 is discretized into N particle elements along the circumferential direction (N is the number of sensors). The upstream particle element moves along the swirl direction and is detected by the downstream sensor, as shown in FIG. Figure 8 As shown in Figure 1, the sensors are divided into two layers, each with N sensors. The particle element moves along the swirl direction from the upstream i sensor to the downstream j sensor. Specifically, according to the size of the sensor, three different installation methods are provided, such as Figure 1 、 Figure 2 and Figure 3 shown.

[0048] The contact process between a particle element and a pipe inner wall sensor is simplified to that between a single particle and a piezoelectric sensor. Using a PVDF piezoelectric thin film sensor, a common type of piezoelectric sensor, as an example, the relationship between particle mass and the voltage signal output by the PVDF piezoelectric thin film sensor is analyzed using particle dynamics and the piezoelectric effect. The complex flow environment in a rotating flow field and the measurement and calculation of the forces acting on the particles are difficult, and not all force conditions can be considered in such a complex environment. Therefore, this section focuses on analyzing the centrifugal force, drag force, friction force, and gravity in the radial, tangential, and axial directions of the particle.

[0049] Radial and tangential forces such as Figure 5 As shown, the movement of particles on the cross section of the pipe is similar to circular motion. At this time, the processor calculates the centrifugal force F exerted on the particles in the particle layer 3 in the radial direction by the following formula: cent and drag force F DN , the drag force F on the particle in the axial direction DA :

[0050]

[0051]

[0052]

[0053] Where: m is the mass of the particle, R is the radius of the pipe, v 切向 is the tangential velocity of the particle, ρ g is the density of the fluid, A p is the frontal area of ​​the particle in the flow field, u sN is the radial velocity difference between the particle and the fluid, C d is the drag coefficient, u sA is the axial velocity difference between the particle and the fluid. Since the velocity difference between the particle and the fluid in the radial direction is small, the radial drag can be ignored.

[0054] The radial force exerted on the piezoelectric film by the particle is equal to the centrifugal force of the particle minus the radial drag force F. N =F cent .

[0055] Therefore, the particles are subjected to drag and friction in the tangential direction, and the formulas are:

[0056]

[0057] F μ =μF N ;

[0058] Where: u sTis the tangential velocity difference between the fluid and the particle, and μ is the friction coefficient of the particle moving on the wall.

[0059] The force exerted by particles on the piezoelectric film in the tangential direction is:

[0060] F T =F DT -μF N ;

[0061] according to Figure 6 and Figure 7 , the particle is subjected to drag force, friction force and gravity in the axial direction. At this time, the axial force exerted on the piezoelectric film is:

[0062] F A =F DA -mg-μF N ;

[0063] Where: m is the mass of the particle, g is the acceleration due to gravity.

[0064] The strains of the piezoelectric film in the radial, axial and tangential directions due to the force exerted by the particles are:

[0065]

[0066]

[0067]

[0068] At this time, using the piezoelectric effect of the piezoelectric film (the piezoelectric film sensor is subjected to force, produces deformation, the internal electric field changes to generate charge, and completes the force-electricity conversion), we can obtain the output charge Q and the output voltage signal U:

[0069] Q=(d 31 ε1+d 32 ε2+d 33 ε3)E PVDF S;

[0070] Where: d 31 d 32 d 33 are the piezoelectric constants of the PVDF piezoelectric film in the x, z and y directions, ε1, ε2, ε3 are the strains of the PVDF piezoelectric film in the x, z and y directions, E PVDF is the elastic modulus of the sensor 2, and S is the area of ​​the piezoelectric film.

[0071]

[0072] Where: C f is the feedback capacitance of the charge amplifier.

[0073] From the above formula, we can see that the voltage output by the charge amplifier is related to the mass m of the particle. At this time, the mass of the microelement particle is:

[0074]

[0075] That is, the relationship between the output voltage and the mass of the particle element.

[0076] At this time, the particle element mass simplified into a single particle is accumulated along the circumference of the sensor arrangement:

[0077]

[0078] Where: m i is the mass of the particle element on the discretized single piezoelectric film, i is the sensor number, and N is the number of sensors.

[0079] The original m obtained is the mass of the particle element. There are N particle elements in a circle of the pipeline. The masses of the discretized particle elements are accumulated. The M obtained at this time is equivalent to the mass of the particles in a circle of sensors arranged on the pipeline.

[0080] Because the gas-solid two-phase flow generates centrifugal force after passing through the cyclone device, it spirals along the pipe wall. Based on the principle of the cross-correlation method, two identical sensors are installed at a certain distance along the measurement path, and their output signals are substituted into the cross-correlation function for calculation. For the upstream and downstream signals x(n) and y(n) measured by sensor 2, the cross-correlation calculation formula after time domain discretization is as follows:

[0081]

[0082] Among them, x(n) and y(n) are the discrete forms of the signals of the adjacent upstream and downstream sensors, W is the total number of signal sampling points, and k is the number of sampling points corresponding to the time delay of the signal flowing through the adjacent upstream and downstream sensors. Substituting different k into the calculation, we can get the function R xy , the time corresponding to the peak value of the function is the transit time τ k .

[0083] The local axial velocity v of the particle along the pipe wall between adjacent upstream and downstream sensors 轴 and v 切 for:

[0084]

[0085]

[0086] where d ij (i=j) is the axial distance between two adjacent upstream and downstream sensors, l ij(i=j) is the tangential distance between two adjacent upstream and downstream sensors;

[0087] Finally, the processor obtains the particle mass flow rate Q in pipeline 1 through the following calculation formula: m :

[0088] Q m =M / τ k ;

[0089] Where: m i is the mass of the particle element on the discretized single piezoelectric film, i is the sensor number, and N is the number of sensors.

[0090] In this embodiment, the air-powder mixture passing through the fixed blades is discretized into N particle elements. During the spiral motion, the element collides with the pipe wall to generate tangential and radial forces, causing the sensor to generate deformation output voltage. The relationship between the element mass and voltage is fitted.

[0091] The mass M of a layer of coal powder is obtained by the accumulation method, and the transit time is obtained by the cross-correlation method to obtain the mass flow rate Q. m .

[0092] Various types of sensors can be used in this embodiment. For measuring the stress of particles on the pipe wall in gas-solid two-phase flow, considering that the pipe wall has a certain curvature, typical flexible stress sensors include the following:

[0093] 1) Piezoelectric flexible sensor: The working principle is to use piezoelectric material as the sensitive layer and measure the pressure through the positive and negative charges generated on the surface of the piezoelectric material after being compressed. When the piezoelectric material is subjected to an external force, it will deform, and at the same time, polarization will occur inside it, causing the positive and negative charges to separate and form charge bonds on the upper and lower surfaces of the material, thereby forming an electric potential difference. The flexible stress sensor based on the piezoelectric effect can effectively convert changes in external force into electrical signals. This sensor is a self-powered sensor. In addition, the piezoelectric flexible stress sensor is extremely reliable, not easily affected by external environmental interference, has a fast response speed, and has stable output performance.

[0094] 2) Resistive flexible stress sensor: The sensing principle is that when subjected to external force, its resistance value also changes accordingly. The pressure exerted on the sensor is calculated by the change in resistance value. The piezoresistive flexible stress sensor has the characteristics of high sensitivity and large monitoring range, and requires an external power supply.

[0095] 3) Capacitive flexible sensor: When subjected to external forces, it will undergo elastic deformation, causing the top and bottom electrodes to shift, thereby changing the relative area and relative spacing of the electrodes, generating a signal output. It has the advantages of simple structure and low hysteresis.

[0096] 4) Triboelectric stress sensors use the friction effect and electrostatic induction principle to convert pressure signals into electrical signals. They have the advantages of fast response speed, high sensitivity, and the ability to convert mechanical energy into electrical energy.

[0097] The number of sensors in this embodiment is adjustable. The number of sensors determines the accuracy of measurement. Two sensors form a group. The number of sensors can be selected when determining the inner diameter of the pipeline and the range of coal powder concentration. Figure 1 、 Figure 2 and Figure 3 All use 18 groups of sensors, with a typical arrangement of 10-25 groups.

[0098] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A method for measuring particle mass flow, characterized in that The steps include: Step 1: Wind powder is transported from bottom to top in a pipe (1), wherein a sensor (2) and a swirl device (4) are provided in the pipe (1), wherein the sensor (2) is mounted on the inner wall of the pipe (1), and the sensor (2) is located above the swirl device (4), and the wind powder passing through the swirl device (4) forms a circular particle layer (3) on the inner wall of the pipe (1); Step 2: The sensor (2) receives the stress signal and transmits the signal to the processor, and the processor calculates the particle mass M on each layer of the sensor on the pipe wall at this time using the following formula: Where: m i is the mass of a single particle element on the discretized piezoelectric film, i is the sensor number, and N is the number of sensors; Step 3: The processor obtains the particle mass flow rate Q in the pipeline (1) by the following calculation formula: m : Q m =M / t k ; Where: τ k is the transit time of particles between two adjacent layers of sensors.

2. The method for measuring particle mass flow according to claim 1, characterized in that Before step 2, the processor calculates the centrifugal force F exerted on the particles in the particle layer (3) in the radial direction by the following formula: cent and drag force F DN , the drag force F on the particle in the axial direction DA , and the drag force F on the particle in the tangential direction DT : Where: m is the mass of the particle, R is the radius of the pipe, v 切向 is the tangential velocity of the particle, ρ g is the density of the fluid, A p is the frontal area of ​​the particle in the flow field, u sN is the radial velocity difference between the particle and the fluid, C d is the drag coefficient, u sA is the axial velocity difference between particles and fluid, u sT is the tangential velocity difference between the particle and the fluid.

3. The method for measuring particle mass flow according to claim 2, characterized in that The processor calculates the force F exerted by the particles on the sensor (2) in the tangential direction by the following formula: T , the sensor (2) is subjected to a force F exerted by the particles in the radial direction N , and the axial force F of the particles acting on the sensor (2) A : F T =F DT -μF N ; F N =F cent -F DN ; F A =F DA -mg-μF N ; Where: m is the mass of the particle, g is the acceleration due to gravity.

4. The method for measuring particle mass flow according to claim 3, characterized in that The processor calculates the output charge Q and the output voltage signal U using the following formula: Q=(d 31 ε1+d 32 ε2+d 33 ε3)E PVDF S; Where: d 31 d 32 d 33 are the piezoelectric constants of the PVDF piezoelectric film in the x, z and y directions, ε1, ε2, ε3 are the strains of the PVDF piezoelectric film in the x, z and y directions, E PVDF is the elastic modulus of the sensor (2), S is the area of ​​the piezoelectric film; Where: C f is the feedback capacitance of the charge amplifier.

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