SU1404827A1 - Device for measuring flow rate of solid particles - Google Patents

Abstract

The invention relates to a measurement technique and makes it possible to improve the accuracy of flow measurement. The measuring section of the gas duct 1 is made in the form of a diffuser 2 coupled with a channel 3 of constant section. In the diffuser 2, the velocities of the particles colliding with the collector electrode 6, which is mounted so that it can move along the longitudinal axis of the measuring section, occur. The working non-insulated surface of the electrode 6 faces the flow. Protection by the isolators of the rest of the current-carrying surface of the electrode 6 and the holder 4 prevents sliding of the particles transported by the gas flow with the electrode 6. The electrode 6 is connected to the signal conversion unit 7 and the recording of the particle flow. 2 Il. (L

Description

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The invention relates to instrumentation and can be used to measure the flow of solid particles (dust suspension) transported by gas streams. Such measurements are necessary in the energy, chemical, mining, metallurgical, food, engineering and other industries.

The aim of the invention is to improve accuracy.

Figure 1 shows the proposed device with the installation of a hemispherical electrode in the diffuser of the measuring section; figure 2 - the same, with the installation of the rod electrode in the channel behind the cone.

A device for measuring the flow of solid particles contains a flue 1, the measuring section of which is made in the form of a diffuser 2, passing into a channel 3 of constant cross section. The measuring section is bounded by the cross sections of the flue, between which a zone is formed, where inhibition of individual fractions of particles occurs. Into the diffuser 2 or channel 3 by means of the holder 4, a collector electrode 6 is inserted through the electrical insulator 5. The front surface of the electrode facing the flow is working. This surface is open to contact with particles transported by the gas flow. The remaining conductive surfaces of the electrode 6 and the holder 4 are protected from direct contact with the insulators by the insulators. A signal conversion and particle flow metering unit 7 is connected to the electric product 6.

The device works as follows.

Through the duct 1 flows rj- flow, transporting polydisperse dust suspension. In the diffuser 2, the velocity of the gas decreases and at the same time the velocity of the particles decreases as a result of the forces of viscous friction of the particles against the gas. The smallest, low-inertia particles move with the gas velocity, large tea cups, having a large mass, continue to move by inertia With a higher velocity, close to the velocity in the duct 1, before the flow inlet into the diffuser 2. In the diffuser 2 there occurs a mismatch of the velocities of particles, each

moves at a speed proportional to its mass and its size. The size of the contact surface of each particle with the electrode and, consequently, the amount of charge transferred to the electrode 6 with the particles, depends on the speed of the collision of particles with the electrode 6 installed in the diffuser 2 or in the channel 3. The amount of charge flowing directly is proportional to the size of the contact surface. To achieve an unambiguous relationship between the flow rate of particles G and the output signal of the device CJ | need to

„R d.

for any size complex --- g

was equal to the same constant value, i.e. if a

W -, E i

  BUT; const

G,

 ZlG; ,

(12)

where B, B are constant coefficients G is the mass flow rate of solid

particles;

(Ji is the output signal of the device; d is the radius of the solid particles.

spherical shape; E is the coefficient that accounts for how many particles incident on the electrode hit with it; . n - exponent; i is the fraction number; W is the particle velocity. Therefore, it is necessary to find the dimensions of the diffuser 2 and position the electrode 6 in such an area of the measuring section where the condition (1) is best performed.

Consideration of dependence (1) indicates that to save A; const, it is necessary that their particle size W decreases with decreasing particle size. This is exactly what is achieved when a polydisperse dust-gas flow in diffuser 2 flows. Thus, it can be seen that the proposed device allows an uncomfortable autocompensation of the effect of particle size on the result of flow measurement by electrical contact. method.

Gas-dynamic calculation of the movement of particles in the diffuser 2, the determination of the coefficient and rate of impact

particles of different fractions with current collector electrode 6 can be performed on a computer by a known technique. Based on the known velocity of the gas flow and particles in the measuring section, the opening angle of the diffuser 2 is chosen (taking into account that the gas velocity in the channel is inversely proportional to the cross-sectional area of this channel) and the location of the electrode 6 is determined. The shape and dimensions of the device can also be determined experimentally.

According to the invention, only the front working surface of the current collecting electrode is kept open for contact with incident particles. The remaining conductive surfaces of the electrode, as well as the electrode holder, must be protected from direct contact with the insulators of the particles. In this way, it is possible to prevent sliding contact of particles with electrode 6. It is known that with sliding contact, the nature of charge transfer changes and the sign of charge can be reversed.

The current removal electrode 6 can be installed both in the diffuser 2 and in the channel 3 of a constant cross section behind the diffuser. The exact location of the electrode is determined by calculation. However, in all cases, the electrode 6 must be located in a measuring section bounded by sections, between which there is a separate -. Particles of particles move with negative acceleration (i.e. with deceleration), since only in this case the effect of

 no fractional composition on the flow measurement result. The electrode 6 should be introduced into the duct 1 through the electrical insulator 5, preventing the leakage of charge from the collector electrode 6 to the walls of the duct 1, which is usually grounded.

In practice, the fulfillment of condition (1) should be achieved for fractions of those particles whose total mass with a given accuracy determines the flow rate of the suspension with different variants of the fractional composition and density of particles on the measuring duct. At the same time for the smallest, albeit numerous particles, and for

 very large, but very rarely;,. occurring in a particular mixture.

condition (1) can be observed with low accuracy or not at all.

Therefore, to optimize

the proposed device predvari; the fractional composition and density of the particulate matter in a particular technological process are revealed, and

also reveal the ranges of possible changes in these parameters over time. Such an analysis is carried out on the basis of operating experience of controlled or similar objects (techno-technological processes) or in the absence of operating experience using known methods of sampling and instrumental examination of samples of suspension under a microscope using weights and

other appliances. All particles whose consumption is to be measured are conventionally divided according to the size and density of the substance into N individual fractions. Each fraction is determined by a characteristic particle having certain parameters G; and p; . Theoretically, an increase in the number of fractions leads to an increase in accuracy (p; density of the material of the particle of the i-th fraction). However, in practice, the allocation is large. the amount of narrow fractions is difficult due to the difficulty of dispersing particles by size. Dispersion can be performed, for example, by centrifuges or using a set of sieves, each of which has cells of a certain size, or other known methods. Usually it is enough to select 5-10 fractions. When the number of fractions is more than 10, an increase in the accuracy of the calculation of the flow metering device becomes insignificant compared with errors caused by other reasons,

As a characteristic particle of this fraction, one should take a particle having an average for a given one; fractions mass.

After the separation of all particles into fractions, it is revealed from among N; those N fractions of particles whose proportion with a given accuracy determines the measured flow rate of particles. In this case, the smallest particles, the mass fraction of which is small, and the total area of contact with the electrode 6 in the case of their collision with it is large, will follow jets of gas flow around the junction (electrode), without colliding with it. and the measurement accuracy will not be affected. Therefore, it is not necessary to take these particles into account in the calculation. Equally, there is no need to take into account large, but very rarely, particles found in this semi-dispersed suspension.

Next, the geometric dimensions of the device (opening angle And the length of the diffuser 2, the shape, size and location of the current-collecting electrode 6) and for — the characteristic particle of each fraction are calculated are calculated by the jj pattern A according to the formula (1). The value of A ;, for each characteristic particle in. the length of the measuring section of the device continuously changes due to the fact that the particle velocity varies from 20 seconds from a speed close to that of the gas in the flue to a speed characteristic of one or another zone of the diffuser 2 (taking into account the influence of local This is -25-spaced electrode 6). The speed of characteristic particles of each fraction and the criterion values at each point of the measuring section of the device are calculated on a computer, taking into account the AOR effect on the particles of aerodynamic and gravitational forces, friction forces, and at high particle concentrations, the forces of interaction between them. In the event that, as a result of the calculation, the value of A; for characteristic particles of different fractions, they differ by an amount exceeding some predetermined, ensuring the established measurement accuracy of the flow rate of 40 particles, are set by the new dimensions of the device and repeat the calculation until satisfactory accuracy is obtained.

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The fractional composition and density of a particulate matter during a controlled process may not remain constant over time. Therefore, for typical variants of the composition, the polydisperse suspension calculates the mass fraction of particles of each fraction from the total mass of particles, which determine the particle consumption with a given accuracy. For example, when controlling the consumption of fly ash emitted with the flue gases of 55 boiler units equipped with electrostatic precipitators, the fractional composition of the ash changes when it is turned off;

35

, 50

,

j 0 5 O 0

five

five

five

0

Research Institute of individual electrostatic precipitator stages. The cases when 100, 75 and 50% of the electrostatic filter stages work can be singled out. At the same time, the weighting factor of each variant of the fractional composition of the particles is evaluated, taking its duration according to the average data for the mean period, for example, for the year of operation of the electrostatic filter. As a result of such an assessment, it may appear, for example, that the operation time of 100% filter stages relates to the filter operation time with 75% stages as 5-1. In some cases, the weighting factor may take into account not only the duration of the variant, but also its importance for con-. controlled process. In the absence of another criterion for assessing the importance of an option, it can be assessed on a five-point scale,

In the measuring section of the device, the section in which the 8-earth electrode 6 is to be installed is revealed. In this settlement, for fractions of particles whose mass with a given accuracy determines their consumption, a minimum is reached.

The indicated minimum is found, for example, by the numerical Method by differentiating the function by coordinates (x, y, z) and determining the site in the cross section of the measuring section, where,

 Er Sp Sp f. (

 : O (p - ratio I Eh Eu 3z

Miyolevo section of the electrode to the section of the measured flow). When the working surface of the current collecting electrode 6 is combined with the indicated platform, the best compensation for the influence of the fractional composition and density of the substance of the particles is achieved. Ensuring a minimum corresponds to the maximum compensation efficiency, since this results in the smallest total deviation A; for characteristic particles of all fractions from the average value of this parameter

 1 f N

N jz;

BUT; -; (3)

-,: §k de oi; - mass production of particles of each fraction from the total mass of particles, which determine their consumption with certain accuracy;

K - the number of typical options for the fractional composition of particles in a gas stream K, 1,2,3, ...,

g is the weight coefficient of each variant of the fractional composition, determined taking into account the mass fraction of each fraction and the weight coefficient of each variant of the fractional composition. The dimensions of the proposed device, which ensure the maximum autocompensation of the effect of the fractional composition of particles, can be found not only by calculation, considered above, but also experimentally.

In the latter case, with different typical versions of the fractional compound and the density of the particle matter in the measuring section of the gas duct, the readings of the measuring device are fixed by moving the collector electrode 6 along the measuring section. Then, considering the results obtained, choose the position of the electrode 6, in which in all modes of operation of the controlled object (taking into account their weights)

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The device readings at the constant consumption of particles undergo the smallest changes. If necessary, repeat the experiment at a different angle of diffuser opening.

To reduce the scope of the experiment, one can first find the position of the electrode by the considered calculation method, and then experimentally clarify its position in the vicinity of the zone identified by calculation.

Claims (1)

Invention Formula A device for measuring the flow of solid particles, containing a measuring section and a collector electrode installed therein, has to be done so that, in order to improve accuracy, the measuring section is filled in the form of a diffuser and a constant cross-section channel connected to it. and the collector electrode is mounted for movement along the longitudinal axis of the measuring section and has an uninsulated working surface facing the flow. Flow