CN109655389B - Method for measuring solid phase concentration in pneumatic conveying pipeline - Google Patents
Method for measuring solid phase concentration in pneumatic conveying pipeline Download PDFInfo
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- CN109655389B CN109655389B CN201910146150.6A CN201910146150A CN109655389B CN 109655389 B CN109655389 B CN 109655389B CN 201910146150 A CN201910146150 A CN 201910146150A CN 109655389 B CN109655389 B CN 109655389B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
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Abstract
The invention discloses a method for measuring solid phase concentration in a pneumatic transmission pipeline, which comprises the following steps: s1, installing a transmitting antenna and a receiving antenna in the measuring pipe section; s2, transmitting microwaves in a circular waveguide formed by a measuring pipe section through a transmitting antenna, receiving microwave signals carrying scattered energy information through a receiving antenna after the microwave signals are physically modulated by scattered energy of a gas-solid two-phase flow medium, and obtaining power signals of the scattered energy through a detector; and S3, calculating the concentration of the solid phase in the gas-solid two-phase flow according to the power signal. The method can accurately obtain the solid-phase concentration parameters of the process, is favorable for automatic control of industrial production, and improves the economy and safety of the industrial process. Can be popularized and applied to other gas-solid two-phase flow and measurement of solid concentration.
Description
Technical Field
The invention relates to the field of solid-phase concentration detection, in particular to a method for measuring solid-phase concentration in a pneumatic conveying pipeline.
Background
Pneumatic conveying is widely used in industrial production sites, particularly in a thermal power plant, pulverized coal enters a hearth through a primary air pipeline to be combusted, due to the difference of pipeline layout and structure, the concentration difference of the pulverized coal in different pipelines is large, inconvenience is brought to combustion adjustment, the economical efficiency of combustion is poor, the combustion efficiency and pollutant discharge are affected, and even the production safety is seriously threatened. The accurate detection of the solid phase concentration in the primary air pipeline is very important, but due to the variability of the power production load and the complexity of two-phase flow, a mature and reliable detection technology is not available at present.
The application of microwave technology to the detection of solid phase concentration of gas-solid two-phase flow has become a research hotspot. In the microwave detection system, microwaves with preset frequency are transmitted in a measuring pipeline, microwave signals can be attenuated and shifted due to the action of solid phases in gas-solid phases, the attenuation and the shift of the microwaves are functions of complex dielectric constants of mixtures, and the complex dielectric constants of the mixtures are functions of components of the mixtures, so that the concentration of the solid phases in the gas-solid phases can be obtained by detecting the attenuation and the shift of the microwave signals.
In practical applications, however, the change of the complex dielectric constant caused by the small concentration change and the millisecond-order response time is very small, and the attenuation and frequency shift of the effect are also very small, so that the sensitivity and real-time performance of the detection system are deteriorated. Microwave-based pulverized coal concentration detection method
At present, the microwave-based coal powder concentration detection method mainly comprises the following steps:
(1) free space attenuation method: CN200710025018.7, microwave measurement system of power plant boiler buggy concentration, a method is published: the microwave generator and the microwave receiver are correspondingly and obliquely arranged along the flowing direction of the pulverized coal at a certain angle. The microwaves are attenuated in the measuring tube by the presence of the coal dust. The concentration of the coal powder can be reflected by measuring the attenuation value of the coal powder. The method can not avoid the influence of the metal pipe wall on the microwave reflection, and has low precision.
(2) Free space reflection (EDITFLOW, germany mucec): the sensor transmits low-energy microwave signals to solid particles in the metal conveying pipeline, and the density of the material is measured by reflected energy of the microwaves. The method is only suitable for the conditions of dense phase flow and pipe diameter less than or equal to 200 mm, and is mainly suitable for coalification enterprises. The primary air pipeline of the power plant is about 600 mm generally, and the precision can not be ensured in practice due to the dilute phase (the concentration of the general mixture is less than 0.5 kg/kg).
(3) The waveguide method comprises the following steps: CN201510745882.9, a setting method of microwave measurement parameters of coal dust concentration, which discloses a method comprising the following steps: the primary air pipe is used as a waveguide, and the change of the dielectric property of the two-phase flow is detected through the change of microwave transmission parameters, so that the concentration of the pulverized coal is obtained. The method has slightly low precision, about 10-15 percent, and can not meet the regulation requirement of 5 percent because of measurement errors caused by scattering and reflection of coal dust particles at the upstream and downstream of a measurement pipeline and changes of coal quality and moisture.
(4) A resonant cavity method: the basic principle is that when a measured medium is placed into a resonant cavity, the resonant frequency and the quality factor are changed, so that the relationship between the density and the dielectric property of the medium and the resonant frequency and the quality factor is established. In the resonant cavity, electromagnetic waves only have the condition of total reflection, other interferences are few, transmission loss is very small, high-precision measurement of density and dielectric characteristics is easy to realize in an application field environment, and the method is obviously superior to all existing detection methods, but the resonant cavity is difficult to construct in practical application and has high realization cost.
Disclosure of Invention
In order to solve the problems, the invention provides a method for measuring the solid-phase concentration in a pneumatic conveying pipeline.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for measuring solid phase concentration in a pneumatic transmission pipeline is characterized by comprising the following steps: the method comprises the following steps:
s1, installing a transmitting antenna and a receiving antenna in the measuring pipe section;
s2, transmitting microwaves in a circular waveguide formed by a measuring pipe section through a transmitting antenna, receiving microwave signals carrying scattered energy information through a receiving antenna after the microwave signals are physically modulated by scattered energy of a gas-solid two-phase flow medium, and obtaining power signals of the scattered energy through a detector;
s3, calculating the concentration of the solid phase in the gas-solid two-phase flow according to the power signal:
s31, calculating the average value of the acquired data after detection:
wherein x is the data acquisition value of the receiving signal of the receiving probe after detection
S32, subtracting the average from the raw collected data:
s33, power calculation:
in the formula, x’(n) data obtained by subtracting the mean value from the original collected data, x’ zcount、x’ fcountAre respectively a sequence x’(n) the number of positive data and the number of negative data, k being a coefficient corresponding to a specific receiving circuit;
s34, concentration calculation:
theoretical demonstration and experiments are carried out to obtain relational data of the scattered signal power value and the concentration, and the obtained data are fitted to obtain the following fitting formula: y = -5.328x3+18.457x2+6.8715x+1E-12；R2Where X is the power value in dBm (decibel-milliwatt), 1E-12 is the meaning of minus twelve power of ten (scientific count), y is the concentration multiplied by 100, in kg/kg;
and multiplying the power value in the above formula by a calibration coefficient k1 (related to pipe diameter) and k2 (related to probe distance) to obtain a powervalue, and substituting the powervalue value into a relation between the scattered signal power value and the concentration to obtain the concentration of the solid phase in the gas-solid two-phase flow.
The invention has the following beneficial effects:
the invention is more suitable for measuring the solid concentration of the dilute phase gas-solid two-phase flow and ensures the precision. In a dilute phase environment, the signal modulated on the fundamental wave is mainly scattering energy, and has a definite relation with the number of solid phase particles (i.e. solid phase concentration). Compared with a free space attenuation method, the strong interference caused by the reflection of the tube wall is avoided; the waveguide attenuation method is too sensitive to coal quality and moisture, and brings considerable measurement errors. Compared with a resonant cavity method, the invention has the advantages of simpler and more practical installation, easier field implementation and lower realization cost.
The method can accurately obtain the solid-phase concentration parameters of the process, is favorable for automatic control of industrial production, and improves the economy and safety of the industrial process. Can be popularized and applied to other gas-solid two-phase flow and measurement of solid concentration.
Drawings
Fig. 1 is a schematic diagram of the installation of a transmitting antenna and a receiving antenna in the embodiment of the present invention.
Fig. 2 is a schematic diagram of the working principle of the present invention.
Fig. 3 is a flowchart of step S3 in the embodiment of the present invention.
FIG. 4 is a graph showing the relationship between the power value and the concentration of the scattering signal in the embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
The concentration of the air-powder mixture in the primary air pipeline of the thermal power plant is less than 0.5 kg/kg, the particle size of the pulverized coal is 90-200 um, and the pulverized coal belongs to typical dilute phase flow. Microwave signals are transmitted in a circular waveguide formed by a measuring pipe section, and due to the existence of a wind-powder mixture, when the microwaves encounter coal dust particles suspended in airflow, scattering phenomena can occur, and the incident microwaves polarize the coal dust particles and are made to forcefully oscillate in a multipole way to emit scattered waves. The scattering power of a particle is related to the frequency of the incident microwave, the size, shape of the particle, and the electrical properties of the particle. When the incident frequency is determined, the scattering of particles depends mainly on the diameter of the particle and the relative size of the incident frequency (wavelength), and can be classified into rayleigh scattering (d < < λ) and meter scattering (d ≈ λ). According to the waveguide theory, the waveguide tube has a cut-off frequency, so the invention uses microwave slightly higher than the cut-off frequency of the measured propagation medium, through installing the transmitting antenna 2 and the receiving antenna 3 (as shown in figure 1) in the measuring tube section 1, the microwave is propagated in the circular waveguide formed by the measuring tube section, the microwave signal is physically modulated by the scattered energy of the gas-solid two-phase flow medium, so that the microwave signal detected by the receiving antenna contains the information of solid phase concentration, and the microwave signal containing the information of solid phase concentration is detected by the detector to obtain the power signal representing the solid phase concentration. According to the power signal, the concentration of the solid phase in the gas-solid two-phase flow can be obtained, specifically, as shown in fig. 3, the method comprises the following steps:
s31, calculating the average value of the acquired data after detection:
wherein x is the data acquisition value of the receiving signal of the receiving probe after detection
S32, subtracting the average from the raw collected data:
s33, power calculation:
in the formula, x’(n) data obtained by subtracting the mean value from the original collected data, x’ zcount、x’ fcountAre respectively a sequence x’(n) the number of positive data and the number of negative data, k being one and the specific receiving circuitThe corresponding coefficients;
s34, concentration calculation:
theoretical demonstration and experiments are carried out to obtain data of the relation between the power value and the concentration of the scattering signal, and as shown in FIG. 4, the obtained data are fitted to obtain the following fitting formula:
y=-5.328x3+18.457x2+6.8715x+1E-12；R2where X is the power value in dBm (decibel-milliwatt), 1E-12 is the scientific count, y is the concentration multiplied by 100 in kg/kg, and in the figure, the abscissa variable is the power value in dBm and the ordinate variable is the concentration multiplied by 100.
And multiplying the power value in the above formula by a calibration coefficient k1 (related to pipe diameter) and k2 (related to probe distance) to obtain a powervalue, and substituting the powervalue value into a relation between the scattered signal power value and the concentration to obtain the concentration of the solid phase in the gas-solid two-phase flow.
Examples
To ensure proper operation of the entire system, some system parameters need to be determined, as shown in table 1:
TABLE 1 System parameters
| Parameter(s) | Diameter of pipeline | Mounting distance of probe | Length of probe | Frequency of transmission |
| 1 | 600mm | 500mm | 240mm | 300MHz |
The experiment is provided with one receiving probe, but the experiment is not limited to this, a plurality of receiving probes can be installed to improve the measurement accuracy, and the installation distance and the installation angle of the probes are all an example of the experiment.
In the embodiment, ten thousand points of data are collected, so that the measurement precision is ensured, the overlong calculation time caused by excessive data is avoided, and the following table shows the collection values of part of received probe signals after being detected.
TABLE 2 data acquisition
In the above table, M represents an omitted part
And (3) calculating the concentration:
(1) data mean value:
the result of the above formula calculation retains the integer part.
(2) Data averaging processing:
(3) calculating a power value:
in the above formula, k takes 2000 and the calculation result is kept as an integer.
(4) The power value in the above equation is multiplied by the calibration coefficients k1, k 2.
(5) Substituting the powervalue value into the relation between the concentration noise signal power value and the concentration:
y=-5.328x3+18.457x2+6.8715x+1E-12；R2where X is the power value, in dBm (decibel-milliwatt), 1E-12 is the scientific count, y is the concentration multiplied by 100, in kg/kg;
the resulting powervalue value was substituted into the fitting equation and the calculated result was 22.21, i.e., 0.2221 kg/kg. In this embodiment, the concentration is defined as: coal powder mass/(coal powder mass + air mass).
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (1)
1. A method for measuring solid phase concentration in a pneumatic transmission pipeline is characterized by comprising the following steps: the method comprises the following steps:
s1, installing a transmitting antenna and a receiving antenna in the measuring pipe section;
s2, transmitting microwaves in a circular waveguide formed by a measuring pipe section through a transmitting antenna, receiving microwave signals carrying scattered energy information through a receiving antenna after the microwave signals are physically modulated by scattered energy of a gas-solid two-phase flow medium, and obtaining power signals of the scattered energy through a detector;
s3, calculating the concentration of the solid phase in the gas-solid two-phase flow according to the power signal, specifically:
s31, calculating the average value of the acquired data after detection:
in the formula, xNThe data acquisition value is a data acquisition value after the received signal of the receiving probe is detected;
s32, subtracting the average from the raw collected data:
s33, power calculation:
in the formula, x’(n) data obtained by subtracting the mean value from the original collected data, x’ zcount、x’ fcountAre respectively a sequence x’(n) the number of positive data and the number of negative data, k being a fixed coefficient corresponding to a specific receiving circuit;
s34, concentration calculation:
theoretical demonstration and experiments are carried out to obtain relational data of the scattered signal power value and the concentration, and the obtained data are fitted to obtain the following fitting formula: y = -5.328x3+18.457x2+6.8715x+1E-12；R2Where x is the power value, unit dBm, 1E-12 is the scientific count, y is the concentration multiplied by 100, unit is kg/kg;
and multiplying the power value in the formula by calibration coefficients k1 and k2 to obtain a powervalue, and substituting the powervalue into a relation between the scattered signal power value and the concentration to obtain the concentration of a solid phase in the gas-solid two-phase flow, wherein k1 is related to the pipe diameter, and k2 is related to the probe spacing.
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