RU2554327C1 - Method for automatic control of continuous flow rate of loose material and device for its implementation - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: material which is freely supplied from a loading hopper by a pressure shaft to a mixing chamber, is mixed with gas in the chamber and is delivered to the output due to the P_m pressure at the input of the output pipeline being measured by a pressure sensor installed in this place as well, the pressure is stabilised at the value determined by the specified flow rate $$Q_{М}^{SP}$$

of the loose material according to the formula $$P_m=A\cdot \exp \left\{B\cdot Q_M^{SP}\right\}.$$

Control continuity is provided due to the fact that the material is supplied to the mixing chamber via the pressure shaft with its height being defined as per the formula $$H_{PS}>\frac{P_c}{(1-\epsilon ){\rho }_M\cdot g}.$$

EFFECT: upgraded accuracy and reliability at simultaneous provision for continuous flow rate control, expanded range of controlled flow rate change.

3 cl, 2 dwg

Description

The task of continuous controlled supply of bulk materials to technological devices as a control action on the parameters of technological processes is relevant for a number of industries in the chemical, metallurgical, food, construction and other industries. Most often, to solve it, they use the method of mechanical movement of material using the working bodies of the feeding and metering devices (belts, impellers, screws, vibrating trays, etc.) [1, 2], the reliability and metrological characteristics of which in contact with bulk media are not comply with the requirements. Controlling the flow of bulk materials by the current weight value becomes ineffective in conditions of variable humidity, causing a significant error. A significant drawback of mechanical feeders and dispensers for bulk materials that implement this method is their high cost, which is determined in most cases by the complexity of the design, dimensions and metal consumption. One of the analogues of the proposed method of controlling the flow of bulk material implements the flow controller according to patent RU 2137173 [3]. The value of the flow rate of bulk materials is set by entering the setpoint corresponding to the pressure force of the flow of bulk material on the force measuring device in the form of a tray associated with a rotary gate providing periodic supply of material to the tray in a predetermined quantity. At a given setting, the gate fluctuates relative to the position corresponding to a given flow rate of bulk material, and the average flow rate of bulk material carried by the air stream is equal to the set value. The reliability of the device is reduced due to the presence in it of a movable element in contact with the flow of bulk material. In addition, the device, in principle, does not provide continuous flow.

Pneumatic feeders and dispensers to control the flow and quantity of bulk materials can be an effective alternative to mechanical systems. However, in most pneumatic systems [4, 5], bulk material is fed by the same mechanical means, which in this case should also provide a given value for the material flow. A known method and device for volumetric pneumatic dosing of bulk materials, devoid of the above disadvantages [6], however, in this case, the material is dispensed in doses of constant volume, and the invention cannot be directly applied to control the continuous flow of material.

Closest to the claimed is a method of controlling flow, implemented using a dispenser of bulk materials for autosvid. USSR No. 530184 [7]. The invention provides uniformity and continuity of the supply of a given amount of material in the air stream. The disadvantages of the device should also include the presence in it of kinematic pairs operating in a flow of bulk material. Mechanical moving parts (plug valve, main control valve and check valve) are subject to abrasion. The ingress of a small fraction of the solid phase into the gaps between mutually moving parts can lead to a violation of the normal operation of the device until the accident. In addition, the pressure sensor is located in the upper part of the mixing chamber, which, in principle, limits the possible range of flow control to the size of the chamber, since the pressure in this zone is not equal in magnitude to the pressure that creates the force moving the particles of the material due to pressure losses in the layer of material located in the camera. In addition to the above, it should be noted that the amount of material in the mixing chamber changes during operation, which leads to a decrease in the accuracy of control implementation.

The purpose of the proposed method of flow control is to increase reliability and accuracy, as well as to increase the range of continuous control of the flow of bulk material.

The inventive control method is illustrated by the circuit of the automatic feeder shown in Figure 1.

, поступающей от задатчика величины давления. Сигнал рассогласования в соответствии с заданным законом регулирования преобразуется в управляющий сигнал µ, величина которого определяет частоту выходного сигнала f частотного преобразователя, управляющего скоростью вращения ω привода воздуходувного агрегата 5.The material from the loading hopper 1 through the pressure shaft 2 under the action of gravity enters the mixing chamber 3, where it is mixed with gas, for example, with the air supplied through the pipe 4 from the blower unit 5. Under the pressure of the air, the two-phase gas-bulk material mixture The transport pipeline 6 is fed into the expansion chamber 7, where due to a sharp drop in pressure, air and solid phase are separated. Dusty air is removed into the suction system, and the bulk material through the exhaust pipe 8 enters the process facility. The pressure P _C at the inlet to the transport pipeline is controlled by a sensor for the current pressure value, the output signal of which is supplied to the comparator, where it is compared with the reference value $$P_{\mathrm{FROM}}^{3D}$$

coming from the set point pressure. The mismatch signal in accordance with the specified regulation law is converted into a control signal µ, the value of which determines the frequency of the output signal f of the frequency converter controlling the rotation speed ω of the drive of the blower unit 5.

The implementation of the proposed control method is possible only if:

сыпучего материала (расходной характеристики);1) the dependence of the pressure P _C from a given flow rate $$Q_M^{3D}$$

bulk material (flow characteristics);

2) dependencies that determine the height of the pressure shaft, which ensures continuous loading of the mixing chamber in the process of issuing the material.

получена в результате обработки представительного массива экспериментальных данных в соответствии с требованиями ГОСТ 14202-69. Эксперименты проводились на полупромышленной установке, основой которой является вертикальный пневматический питатель (ВПП) для сыпучего материала, реализующий заявляемый способ управления. На рисунке 2 приведен пример экспериментально определенной расходной характеристики ВПП для определения требуемой величины давления P_C по заданному значению расхода сыпучего материала. В качестве последнего в данном случае использовалось сухое шлифованное пшено с диаметром частиц d_M=(2±01)·10^-3 м, и плотностью ρ_M=1100 кг/м³. Соотношение диаметров частицы и внутреннего диаметра транспортного трубопровода d_M/d_TP=1/10. Газ-носитель - воздух при нормальных условиях.It should be noted that the specificity of this control method does not allow applying mathematical models known from the theory of pneumatic transport to it. Dependence $$Q_M^{3D}=f\left(P_{\mathrm{FROM}}\right)$$

obtained as a result of processing a representative array of experimental data in accordance with the requirements of GOST 14202-69. The experiments were conducted on a semi-industrial installation, the basis of which is a vertical pneumatic feeder (runway) for bulk material that implements the inventive control method. Figure 2 shows an example of an experimentally determined flow characteristic of the runway to determine the required pressure value P _C from a given value of the flow rate of bulk material. As the latter, in this case we used dry polished millet with a particle diameter d _M = (2 ± 01) · 10 ^-3 m and a density ρ _M = 1100 kg / m ³ . The ratio of particle diameters and the inner diameter of the transport pipeline d _M / d _TP = _1/10 . Carrier gas is air under normal conditions.

The approximating equation for the flow rate characteristic has the form

where A and B are empirical coefficients whose values are determined by the parameters of the solid phase, air and the design parameters of the feeder.

The height of the pressure shaft H _NS is determined by the formula

where P _K is the pressure in the mixing chamber at the outlet of the pressure shaft;

ε is the porosity of the column of bulk material in the pressure shaft;

g is the acceleration of gravity;

ρ _M is the density of particles of the material.

The use of this expression is based on the fact that the material in the pressure shaft is saturated with air and its porosity is different from the porosity of a freely poured material. The fulfillment of condition (2) allows continuous loading of the mixing chamber without stopping the delivery of material.

The main advantages of the invention in comparison with the prototype are as follows:

- provides continuous control of the flow of bulk material in a wide range, as well as increased accuracy of converting the control signal into a change in flow rate by selecting the optimal pressure selection point;

- there are no kinematic pairs working in contact with bulk material, which increases the reliability of the feeder;

- provides continuous loading of the feeder material in the process.

Information sources

1. Vidineev, Yu.D. Automatic continuous dosing of bulk materials. / Yu.D. Vidineev. - M .: Energy. - 1974. - 120 p.

2. Pershina S.V. Weight dosing of granular materials / S.V. Pershina, A.V. Katalymov, V.G. Alone, V.F. Pershin. - M.: Mechanical Engineering, 2009 .-- 260 p.

3. The regulator of the flow of bulk materials. Patent RU 2137173.

4. Katalymov A.V. Dosing of bulk and viscous materials / A.V. Katalymov, V.A. Lyubartovich. - L .: Chemistry, 1990 .-- 240 p.

5. M.P. Kalinushkin. Pneumotransport equipment: Reference book / Under total. ed. M.P. Kalinushkina. - L .: Engineering, 1986.

6. The method of volumetric dosing of bulk materials and a device for its implementation. Patent RU 2503932 C2

7. Dispenser of bulk materials. AU USSR 580184.

Claims (3)

1. The method of continuous control of the volumetric flow rate Q _{M of} bulk material, which consists in the fact that the material freely flowing through the pressure shaft from the feed hopper into the mixing chamber is mixed in it with the gas supplied through the aeration pipe and is discharged through the exhaust pipe and installed on an expansion chamber under the action of gas pressure, characterized in that the gas pressure P _C is measured at the inlet to the exhaust pipe, and the pressure is adjusted in accordance with a predetermined flow rate Applicability:

Where

- the set value of the volumetric flow rate of bulk material, and the coefficients A and B are determined by the parameters of the exhaust pipe, bulk material, as well as the ratio of these parameters. 2. A feeder for continuous control of the flow of bulk materials, implementing the control method according to claim 1, comprising a feed hopper connected to the mixing chamber by a pressure shaft, an aeration pipe, an exhaust pipe connected to the mixing chamber, a pressure sensor and a pressure regulator, characterized in that it contains a frequency converter, a blower unit with a drive connected to the aeration pipe, and a pressure value adjuster enny to the controller, wherein the pressure sensor is installed at the inlet to the outlet conduit. 3. The feeder according to claim 2, characterized in that the height of the pressure shaft is determined by the formula

where P _K is the pressure in the mixing chamber at the outlet of the pressure shaft;
ε is the porosity of the column of bulk material in the pressure shaft;
ρ _M is the density of particles of the material.

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