RU2503932C2 - Method for volume dosing of loose materials and device for its realisation - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: dosed material freely arrives along a discharge shaft from a loading hopper into a mixing chamber, is mixed there with gas and supplied to the outlet under action of pressure of this gas into a control object. The material flow is proportionate to gas pressure, at the same time according to the invention the specified volume of the material is previously measured in the mixing chamber. During the time of chamber filling the gas is not supplied in it, and process of loose material supply to the outlet the pressure of gas is maintained permanent and higher than the pressure of the material column in the discharge shaft. The gas flow during material discharge corresponds to the doubled suspension velocity of material particles.

EFFECT: higher accuracy and reliability of dosing, reduced power inputs for material movement.

4 cl, 4 dwg

Description

The invention relates to the field of dosing bulk materials, and can be used in chemical and related industries, as well as in the production of building materials for supplying a given amount of substance to technological control objects.

Dosing of bulk materials in industry is currently most often carried out by weighing batchers with movable working bodies (tape, screw, drum, etc.) or using weighed containers periodically emptied into the control object. The weighing method for dosing bulk materials under industrial conditions is associated with significant errors, mainly determined by the uncontrolled change in the moisture content of the material. In addition, the aforementioned dispensers that implement the weighing method of dispensing, contain a significant number of kinematic pairs in direct contact with bulk materials, often with abrasive properties.

Significant advantages in terms of metering accuracy and reliability are provided by a pulsed volumetric metering method, in accordance with which a predetermined amount of bulk material is transported by a gas stream. This method is described in the literature (for example, [1], p.145-148 and [2], p.158-161), and is also implemented in accordance with a number of inventions protected by patents. In particular, as an analogue of the claimed one, one can consider a method and a device for feeding raw materials to an electrolytic bath, in which the dispenser has two independent aeration channels, one of which is used to fill the measuring chambers - pipes, and the other - to dump the accumulated doses through the guide tubes of the punches on the crust of the electrolyte (US 3901787, NIIZEKI et al., 204/245, 08/26/75). The invention (SU 1611993 Al, Tajik Aluminum Plant and others, C25C 3/14, 07.12.90) also describes a device for powering an electrolyzer, in which alumina is supplied to and dispensed by a pneumatic chute and an aeration system. In this case, the magnitude of the delivered dose is unchanged (1-2.5 kg) and is determined by the volume of the dispenser and the bulk weight of alumina.

The method of supplying aluminum electrolyzer with alumina and corrective additives (patent RU 2121529, publ. 10.11.1998), which includes the dosed supply of granular material from the tank into the electrolyte melt by means of pneumatic pulses with controlled parameters, provides for the material to be cut off when adjusting the dose due to self-locking of the outlet after stop feeding aerating pneumatic pulses.

The disadvantage of the above technical solutions is the presence in the dosing system of movable elements (rods, hinges, etc.) that have direct contact with bulk material. In the latter case (US Pat. RU 2121529), in addition, the dose value is determined only by the duration of delivery of the material through the discharge gap, which reduces the accuracy of measuring the dose in comparison with the weight or volume dosing methods.

By A.S. SU 530184, which is the closest analogue (prototype) of the proposed dosing method and device for implementing this method. The main elements of the prototype (figure 1) are: loading hopper 1, pressure shaft 2, mixing chamber 3, gas supply pipe 4, exhaust pipe 5, electric actuator 6, pressure switch 7, control system 8, peristaltic valve 9, and also plug crane 10. The entrance to the chamber 3 from the pressure shaft 2 is blocked by the check valve 11. Material flows by gravity from the hopper 1 into the chamber 3, where it is mixed with air continuously supplied to the chamber and transferred through the exhaust pipe 5 to the control object. Material is discharged in a continuous stream of a two-phase mixture. The concentration of the solid phase is regulated by changing the flow area of the peristaltic valve 9. The size of the flow area of the valve 9 is regulated depending on the set pressure in the chamber using a pressure switch 7 connected through the control system 8 to the electric drive 6. The value of the instantaneous flow of material at the outlet of the dispenser is determined the degree of opening of the valve 9 and, as the authors claim in paragraph 5 of the description of the invention, the pressure in the chamber 3.

The dispensing method implemented by this device has a number of significant disadvantages.

The disadvantage of this dosing method is, first of all, the presence of systematic and random dosing errors. The source of systematic error is the change in the total height of the material column in the feed hopper and pressure shaft. This material is more or less saturated with air, and, therefore, the main law of hydrostatics P = ρ · g · H is applicable to it. In the process of emptying the hopper, the height of the material in it decreases continuously, which leads to a constant decrease in pressure in the chamber. The latter, as shown above, determines the amount of material entering the chamber at the same degree of opening of the throttle control body 11. The source of the random component of the metering error for the prototype and similar devices is the gas temperature. When the temperature changes, the load-bearing capacity of the gas changes due to changes in its density and viscosity, therefore, the amount of material transferred also changes uncontrollably.

The disadvantage is that the implementation of this dosing method requires the presence of movable elements (9, 10, 11) directly in contact with the bulk material, which significantly reduces the reliability.

Another disadvantage of the prototype is that the air supply to the dispenser is continuous, because air consumption is correlated with material consumption. This mode is associated with unreasonably high energy costs for moving the material, since there is no possibility of working in an energy-saving mode.

A method of volumetric dosing, which avoids the above disadvantages.

The purpose of the invention is to improve the accuracy and reliability of dosing, as well as the optimization of specific energy costs.

This goal is achieved by the fact that dosing is performed in a pulsed mode with volumetric metering of single doses. The essence of the proposed method of dispensing bulk material is illustrated in figure 2.

The dosed material under the action of gravity comes from the feed hopper 1 through the pressure shaft 2 into the mixing chamber 3, which also serves as a measuring tank. Loading continues until the natural filling of the mixing chamber. The dose volume is determined by the size of the chamber, the angle of repose, and the bulk density of the material. Then, gas is supplied through the gas supply pipe 4 to the measuring tank. The material enters into a fluidized state and is discharged in the gas stream through the exhaust pipe 5. In this case, the gas flow rate is fixed and such that the pressure in the mixing chamber is obviously greater than the pressure of the column of liquefied material in the pressure shaft. Thus, during the dose, the material does not enter chamber 3. After the completion of the dose, the pressure in the chamber 3 drops, which is a signal to stop the gas supply. At the same time, there is a natural filling of the container with material under the action of gravity. The dispenser is ready to dispense the next dose. The time-average mass flow rate of a material when several doses are dispensed is defined as

Here, M ₀ is the mass of the dose, f and T are the frequency and period of the dose, respectively.

Studies of the layout of the dispenser that implements the proposed method for dispensing bulk material were conducted at the Department of Automation of Chemical Processes of the St. Petersburg State Technological Institute (Technical University). As the dosed material, spherical granules of organic matter having a diameter of d _M = (2.0 ± 0.1) · 10 ^-3 m and a density of ρ _m = 1200 ± 70 kg / m ^{3 were used} .

It is experimentally confirmed that the dependence of the specific cost of carrier gas per unit mass of bulk material F _B / F _M on the absolute value of the gas flow rate F _B has a minimum (Fig. 3). Dependencies are given for three values of one of the design parameters of the dispenser.

It was also determined that the minimum specific flow rate occurs at the absolute value of gas flow rate, with a certain degree of accuracy of the corresponding doubled speed of rotation ν _BT for particles of bulk material. The same value of the carrier gas velocity is recommended by various sources, in particular, [4, 5] as the rate of stable transportation.

Thus, for the implementation of the proposed dosing method, the following conditions must be met.

1. In order to hold the material in the pressure shaft during dose delivery, the pressure P _K in the mixing chamber 3 must be definitely greater than the pressure P _{C of the} column of fluidized material in the pressure shaft:

2. In order to minimize the specific energy consumption when issuing a dose and ensuring stable transportation of bulk material, it is necessary that the carrier gas consumption during material issuance be constant and correspond to twice the speed of rotation for particles of the material to be dosed:

Based on relations (2) and (3), an a priori one is possible, based only on a given value of the average material flow rate F _CI> , particle sizes and density, as well as gas density and viscosity, calculation of parameters of the metering unit and blower machine.

To implement the described dispensing method, an automatic pulsed volumetric dispenser of bulk materials is proposed (Fig. 4).

The dispenser contains a loading hopper 1 connected by a pressure shaft 2 to the mixing chamber 3. The dose is dispensed through the exhaust pipe 5. To supply air to the measuring tank through the aeration pipe 4, an electric blower unit 12 is used 6. The pressure in the mixing chamber 3 is controlled by a relay pressure 7, the output signal of which through the control system 8 is supplied to the actuator 6 of the blower unit 12. Device 13, which is a section of the pressure shaft, for example, made in the form of a bellows, p It is designed to move the discharge section of the pressure shaft relative to the bottom of the mixing chamber in order to pre-adjust the dose volume. An expansion chamber 14 is installed at the outlet cut of the exhaust pipe.

The device operates as follows. At the initial time, the drive 6 of the blower assembly 12 is de-energized, and the measuring tank 1 is filled by free flowing material along the pressure shaft 2 with bulk material. The volume of material in the initial position in the tank is determined by its size and angle of repose of the material. When applying an external signal for the dose, through the control system 8, the drive of the blower unit is turned on, and gas is supplied to the tank 1. The gas parameters correspond to conditions (1) and (2). Particles of solid material are picked up by the stream and, as part of a two-phase mixture, leave the mixing chamber through the exhaust pipe 5. When leaving the exhaust pipe, the two-phase mixture enters the expansion chamber 14, where the pressure drops. Material under the action of gravity moves to the outlet of the dispenser, and dusty air is carried into the suction system. In accordance with condition (1), in the process of dispensing the dose, material does not enter the mixing chamber through the pressure shaft 2. After emptying the measuring tank, the pressure in it drops to a value determined by the pressure loss on the empty exhaust shaft, which causes the pressure switch 8. The pulse from the relay 8 through the control system 9 turns off the drive of the blower unit. The mixing chamber is again filled with material. The dispenser is ready to dispense the next dose.

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

- there is no error in the dose from a change in the height of the column of material in the pressure shaft;

- there is no error in the dose due to changes in the temperature of the carrier air;

- the dispenser does not contain movable elements (kinematic pairs) in contact with bulk material, i.e. has increased reliability;

- dosing is carried out in conditions of minimizing the specific energy consumption for the issuance of a unit mass of the dosed material.

The processing of the results of repeated repeated measurements of the dose, performed during testing of the layout of the inventive device, showed that the relative error of the unit dose, determined by weight, does not exceed 1.7% (figure 5).

LITERATURE

1. Pneumotransport equipment: Reference book / Under the general. ed. M.P. Kalinushkina. - L .: Engineering, 1986.

2. A.V. Katalymov, V.A. Lyubartovich. Dosing of bulk and viscous materials. - L .: Chemistry, 1990.

3. P.N. Dmitriev, V.T. Prokopovich. Bulk material dispenser. A.S. No. 530184. Published September 30, 197, Bulletin No. 36.

4. Goloburdin A.I., Donat E.V. Pneumatic transport in the rubber industry. - M., Chemistry, 1983.

Brief description of diagrams and figures

Figure 1 - Scheme explaining the inventive method of dispensing, where: 1 - loading hopper; 2 - pressure shaft; 3 - mixing chamber; 4-pipeline for gas supply; 5 - exhaust pipe.

Figure 2 - Dependence of the specific costs of the carrier gas from the absolute value of the gas flow.

Figure 3 - Pulse volume automatic dispenser of bulk materials, where:

1 - loading hopper; 2 - pressure shaft; 3 - mixing chamber; 4-pipeline for gas supply; 5 - exhaust pipe; 6 - electric drive; 7 - pressure switch; 8 - control system; 12 - blower unit; 13 - a device for preliminary adjustment of the dose; 14 - expansion chamber.

Figure 4 - Dependence of the mass of the dose, measured by the volumetric method, on the speed of the carrier air.

Claims (4)

1. The method of volumetric dosing of bulk material, which consists in the fact that the dosed material, freely flowing through the pressure shaft from the loading hopper into the mixing chamber, is mixed with gas and fed to the outlet under the influence of the pressure of this gas into the control object, and the material flow is proportional gas pressure, characterized in that, in order to improve the accuracy and reliability of dosing, as well as to reduce the cost of electricity for moving the material, a given volume of material is pre-measured in cm the chamber, and during the filling time of the chamber, gas is not supplied to it, and during the supply of bulk material to the outlet, the gas pressure is kept constant and greater than the column pressure of the material in the pressure shaft, while the gas flow rate when the material is discharged corresponds to twice the speed of particles material. 2. Pulse volume automatic dispenser of bulk materials that implements the dispensing 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, and a pressure switch, characterized in that it contains a blower unit with a drive, the pressure switch being connected to the drive of the blower assembly. 3. The dispenser according to claim 2, characterized in that an expansion chamber is installed on the output section of the exhaust pipe. 4. The dispenser according to claim 2, characterized in that the pressure shaft is movable along the vertical axis with the possibility of changing the distance from the output edge of the shaft to the bottom of the mixing chamber.

Images