HU191615B - Method for separating granular material masses in components - Google Patents

Abstract

Components of various substance qualities may be conveniently separated by an electrostatic field even if the components present in a stationary electrostatic field no difference of behaviour enabling their separation. An electrode mounting (8) is arranged facing the carrier surface based on dielectric material of the transport path (3). Under the transport path (3) there are provided one or a plurality of divided reception containers (6, 7). An electrostatic charge is produced on the carrier surface. The agglomerate stored in bulk is continuously supplied to the carrier surface. Between the carrier surface and the electrode mounting direct voltage pulses are introduced. The plant comprises a transport path (3) with a carrier surface consisting of dielectric material, a mounting of electrodes (8) arranged facing the carrier surface, a correspondingly divided reception space (6, 7), as well as a pulse source and a supply device.

Description

BACKGROUND OF THE INVENTION The present invention relates to a sorting process for sorting particulate matter by component using a crown discharge, wherein the material exhibits a different cgycdeinck exhibiting a different electric polarity, a zero-mean, high-voltage pulse, and a different electric field.

High voltage separation is a widely used method. This is also referred to in the literature as electrostatic separation. According to the state of the art, the separation of granular material assemblies of individuals of different material quality is based on two properties:

(a) different electrical conductivity,

b) different morphological (shape) features.

A common feature of prior art high-voltage separation processes is that the material applied to the electrically conductive tape or roller, which is grounded, in most cases insulated, has a polarity (in most cases it has a negative potential). ), passes under the corona discharge electrode, where it is electrically charged and adheres to the tape or cylinder (hereinafter referred to as the support surface) due to the attraction between the electrical charge of the particles and the influent (mirror) charges of the grounded electrode.

Various solutions are used to feed the corona discharge polarity constant polarity. Mostly, the power supplied by the 59 or 60 Hz mains voltage is either filtered or non-filtered DC power supplied by a single or two-way rectifier, but power is also provided by other known solutions with constant polarity pulses of frequency, amplitude, and pulse width.

In the case of (a) above, different individuals of the material behave differently, leaving out the electric field of the corona discharge electrode. Particles with a higher electrical capacity transfer their charge from the crown charge to the substrate faster, so that the attraction between the influent (mirror) charge of the self and the grounded electrode is also reduced.

Thus, particles of higher electrical conductivity leave the substrate surface earlier than the inferior conductivity due to the combined effect of gravity and centrifugal force. Methods based on these are described e.g. U.S. 2,072,501; US 2,314,940; U.S. 3,308,948; U.S. Patent Nos. 4,116,822.

Conductivity! There are two known methods for increasing the resolution of the on-line separation.

In one method, the material is transferred from the electrode for crown-filling and patching to a substrate which produces a spatially separate ac-corona discharge, whereby, over time, a positive and negative polarity charge occurs in the same frequency as the electrode feed frequency.

Pre-charged particles, due to the nature of the electric forces, charge only from space-filling waves opposite to their crown charge, so that the resulting charge, which causes them to adhere to the substrate surface, is reduced.

The greater the reduction, the greater the dielectric permittivity of the particle. As the permittivity of the metallic particles is higher than that of the insulating material, during treatment the metallic particles will be removed from the substrate earlier than with the insulating material. Such a solution is described in U.S. Pat. No. 3,970,546. patent specification.

Therefore, it is important to note that the particles in the AC corona discharge electrode, regardless of material quality, will be subjected to a force whose average time increases the degree of adhesion of the particles to the carrier.

The other method has been developed for the separation of particles of powdery particles (about φ 0.075 mm in diameter) that are susceptible to floating. Because of the small particle size of these mixtures, the electrical forces are greater than the inertial forces, so that, after detachment from the substrate surface, the particles can enter and move under the action of the crown electrode, thereby impairing the resolution of the separation.

This phenomenon can be eliminated by lowering the mean electric field strength over time.

The reduction of the mean field strength (with unchanged crown charge) is achieved by feeding the electrodes with pulse voltage. The magnitude of the mean value can be varied by the shape of the pulse and its fill factor.

Such a procedure is described in German Patent Application No. 12,742,522. Publication Document: The corona filling electrodes are supplied with rectified pulse voltage.

In the case of (b) above, the components of the charged particulate material are of different shapes (mostly one flat and elongated, the other spherical) and therefore, due to their degree of charge and partly due to the different nature of the contact surface geometry substrate.

The flattened elongated particles adhere more strongly to the substrate surface and the charge reduction due to their own electrical conductivity after charging leads to a reduction in the adhesive force to such an extent that the particles are detached by the combined effect of gravity and centrifugal force. The spherical particles, due to their charge loss due to their own electrical conductivity, are removed from the substrate surface faster than the flattened particles. There are two main physical causes for better adhesion of flat particles. On the one hand, the transverse surface of the flattened particles into the electric space is larger than that of the spherical form, and thus they are more charged because the charge obtained during the crown charge is proportional to this surface. On the other hand, due to the flattened nature, the charge of the particle is closer to that charged in the grounded electrode, so that the electrical force of adhesion will be higher.

191 61Ε

Such a process is described in U.S. Pat. No. 4,251,353. patent specification.

It also follows from the foregoing that prior art processes are not capable of separating particles of particulate material from an electrically conductive material class (electrically conductive or electrically insulating) having particles of approximately the same electrical conductivity, approximately the same shape and mass. This is the case, for example. in the case of a mixture of sunflower seed with sclerotinia sclerotiorum.

The present invention is intended to separate individuals of such sets of materials per component.

A preferred field of application of the invention is the separation of particulate media utilized in agriculture, e.g. sets of seeds and fossilized fungal formulas, purification of seeds, quality classification of seeds.

Once the essential features of the process have been described, one skilled in the art will recognize that other areas of the art. It may also be advantageous to use the invention in all cases where the constituents of the particulate material exhibit different temporal behavior in an electric field generated by alternating polarity, zero-mean, high-voltage pulses.

The present invention is based on the discovery that mixtures which exhibit similar behavior in high-voltage electrical fields of constant polarity do not necessarily behave in a similar manner in a high-voltage electrical field generated by a series of pulses of variable polarity and preferably chosen; we can make use of the fact that the dielectric polarization of individuals in the case of impulse-like spatial variation only after a certain - material type - delay time ^! sets to the steady-state value for the new spatial relation, for both spatial polarities.

If we consider this phenomenon in combination with two other phenomena, on the one hand, by creating a corona discharge only in one (in our case negative) spatial polarity, the particles begin to charge at the instantaneous polarization according to the space charge concentration and charge carrier mobility. to a level determined by their condition; furthermore, in the case of the other (in our case positive) polarity, the electric field on the particle surface - thereby the charge loss due to the finite electrical conductivity of the particle - is also affected by the current polarization state; we will be able to perform the separation in a new and more efficient way than before, based on characters not yet utilized in breeding technology,

Therefore, according to the invention, the electrodes are connected to a pulse voltage of alternating sign, wherein the half-periods of opposite polarity have different durations and amplitudes, while in the opposite-polarity half-times the product of the voltage and time areas is equal, i.e.

The new process will be described in more detail by means of figures.

Figure 1 schematically illustrates an exemplary apparatus for carrying out the process of the invention. 2-4. Figures 3 to 5 illustrate the mechanism of action of the invention

Referring to Fig. 1, a circular conveyor 3 is formed: it is a metal cylinder encased in an insulating layer on a bearing earthed mantle which is rotated by a variable speed drive 9 in a clockwise direction. Above the conveyor 3 is a feeding device consisting of a mixing container 1 and a vibrating feeder 2 which is fitted thereto.

Opposite to the periphery of the conveyor track 3, an electrode array 8 is formed along a suitably chosen arc length of thin metal wires 0.3 mm in diameter parallel to the cylinder axis. Connected to the electrode array 8 is a voltage source 10 having a polarized, polarized, high-voltage pulse of medium-polarity variable peak frequency, shape, and fill factor.

Below the conveyor 3 is located a receptacle divided into spaces 6 and 7, to which is attached an adjustable inclination baffle 5.

On the opposite side of the conveyor track 3, opposite to the cutting wire 8, is a grounded brushed metal brush 4 which is in frictional contact with the support surface.

The mode of operation of the described apparatus is investigated when the components of the mixture to be separated are sunflower meadow and sclerotinia sclerotiorum.

The particles in the mixing container 1 are continuously fed by the dispenser 2 to the peripheral point 3a of the conveyor 3.

The rotating roller conveys the particles into the electric field created by the electrode array 8. The electric field is excited by time-varying polarity, zero-mean, high-voltage pulses. The peak value of one half-period of the pulse-like high voltage (in this case, the negative polarity path) is selected higher than the peak value of the other half-period. This ensures that the corona discharge occurs only in one half-period, i.e. the charges arising from the corona discharge are always of the same sign, while the particles are exposed to a highly variable field electric field.

In this electric field, individuals behaving differently with respect to the temporal variation of dielectric polarization (hereinafter referred to as "dielectric polarization") behave differently. The healthy sunflower meadows move on to the grounded substrate surface and then, out of the electric field, due to their finite electrical conductivity, gradually transfer their charge to the substrate surface under the combined effect of weight and centrifugal force and fall into the second 6 compartments. The non-exchanged particles Ic are separated by the brush brush 4 which also prevents any filling of the insulating surface.

The sclerotinia sclerotiorum, on the other hand, is partially non-adherent to the excited space, and its path is affected by the characteristics of the excitatory voltage pulses, so that they can only fall into the first 7 spaces of the vessel.

By adjusting the array of electrodes 8 along the arc and the position of each electrode, the distance between the substrate and the electrodes can be modified, and the angular position of the arc formed by the electrodes can be changed along the periphery of the drum; changing the rotational speed can alter the combined effect of the gravity and the centrifugal force and thereby the location of the separation; By adjusting the angular position of the baffle plate 5, it is possible to adjust the optimum separation separation according to the particular mixture.

The mode of action of the invention will now be examined in more detail.

The process is followed for a period of a pulse sequence.

Let T be the period time of the pulse sequence and select the starting time of the test so that the first half-period Ti is negative (the wire electrodes of FIG. 1 are negative) and the half-period Ti <t <T is positive (the wire electrodes of FIG. positive relative to the grounded substrate) the electric field strength generated by the electrode array 8 of Figure 1.

According to the invention, the excitation voltage is selected such that it is capable of producing a corona discharge in the space below the electrode array 8 in the first half period and in the second half period.

The evolution of the force field in the first half period is illustrated in Figure 2, which shows a wire electrode of an array of electrodes 8 and a grounded supporting surface facing it. Due to the small radius of curvature of the wire electrode, a very high field strength is produced in the immediate vicinity of the wire. There is always a small number of positive and negative ions in the air around the wire, which exerts a force proportional to the magnitude of the field.

Thus, in the space shown in Figure 2, the negative ions travel to the positive electrode, the positive ions to the negative wire electrode in the given arrangement, the negative ions decreasing, and the positive ions increasing. The latter break up (ionize) with the neutral air molecules and collapse into positive and negative ions. This phenomenon is the crown discharge, which produces the charge distribution shown in Figure 3. The number of ions in the cloud per unit volume of negative space charge in front of the surface of the cylinder carrier depends on the magnitude of the field and on time (Tj).

Let us now look at the phenomenon of dielectric polarization, which is illustrated in Figure 4. During the first half-period, the charge is separated on the particle placed in the force field as shown in the figure. Charge separation is not instantaneous but occurs with a certain time delay.

The time characteristic of the delay, the so-called. time constant characteristic of the particle material.

The crown charge occurs such that the positive polarized charges of Figure 4 attract the negative ions of the charge cloud of Figure 3. The particle will thus be negatively charged. Since negative ions only reach the particle after a certain time, this charge process also has a characteristic time constant, the magnitude of which depends on the charge concentration and the mobility of the negative ions. Thus, the particle charge process has two time constants. one of which is material and the other is space control. describe the increase in charge over time as O <<t <T, the time function Qi (t) in the half period, and let Ej (t) be the field strength in the same half period at the particle location, then for the particle

F, (t) = OiO) Ei (t) will be subjected to a CD force which, as is easy to see, holds the particle on the substrate.

In the half period T, <t <T, the direction of the field strength is reversed. The force acting on the positive and negative ions of Figure 3 will now move the ions toward each other, which will recombine and the space charge will disappear. As the field strength is not sufficient to ionize the air during this half-period, no further field charges are generated. The corona discharge is interrupted. The particle will polarize in the opposite direction to that shown in Fig. 4, delayed by the time constant mentioned earlier.

The force field of the thus polarized charges is superimposed on the force created by the wire electrode and obtained by the particle in the preceding half-period: the charge generated by the crown charge. This results in a change in the field strength of the particle inside and on the surface due to polarization and thus the polarization indirectly affects the finite electrical conductivity of the particle per unit of time transmitted to the substrate! charge. This in turn means that the particle charge loss process will also be polarization dependent, i.e. the discharge process will also be characteristic of the particle material through the polarization phenomenon. describe the decrease in particle charge over time in the positive half-period Tj, <t <T by the Q ₂ (t) function. If the field strength at the particle location is E ₂ (t) during the same half period, then the particle

F ₂ (t) = (ΜΟΕ, Ο) (2) will apply a force that now wants to remove particles from the substrate.

The average force acting on the particle during the entire 0 <t <T period is ~ 1 ^T

F = ψ f ÍF, (t) + F ₂ (t) Jdt (3) o

expression.

From the above equations we get that

Γ T T Ί

F = | / 9, (t) E, (t) dt + f Q ₂ (t) E ₂ (t) dt lo t, J (4)

191,615

Given that Qi (t) and Q ₂ (t) are constant (negative) signs in the interval O <t <T, we can apply the mean of the integral calculation to:

ιΓ ^{Ti Tj} 1

F = / E, (t) dt + Q ₂ / .E ₂ (t) dtJ (5)

Here and Q _{2 are} the mean values of the charge in the negative and positive half-lives.

Given that the excitation voltage is zero mean, so

TT f ¹ E ₂ (t) dt = - / 'E, (t) dt (6)

T o

Put this into our former equation that

T, / Atodt p = - ° - ~ _T - (Q, - fe), which shows that in the case of Oj>, the particle adheres to the substrate surface, whereas in Q, <fe, it is detached solely by the action of electric forces.

Since, for a given field excitation, the polarization phenomenon is a material-specific jetbet process such as Q, (t) and Q ₂ (t), and therefore, He and fe will become material-specific quantities.

Consequently, the luting or material quality for separation will be dependent phenomenon. ~ AdoU behind our example sunflower kaszatra Q _4> Q _2, Sclerotinia sclerotiorumra and Q _<Q2 condition will be met in case térgerjesztés suitably selected.

A prerequisite for the mechanism of action is therefore that for a suitably chosen alternating polarity zero-mean field excitation, different types of particles respond with different dielectric polarization - and therefore different charge and discharge histories.

The shape of the response functions can be influenced by the shape, frequency, fill factor (TJT ratio) of the excitation voltage, the arrangement of the electrodes, the subtraction of the substrate cylinder surface, and the rotational speed of the drum. In the case of the equipment implemented and described schematically above, the above-mentioned intervening quantities have varied within the following limits:

- earthed cylinder diameter: 200 <ψ <250 mm, - cylinder speed: 5 <n <60 / min, - negative peak excitation voltage: 10 <<u <60kV, - positive peak excitation voltage: 2 <

<U <10kV, j - frequency of excitation voltage: 10 <f = γ <<500 Hz, - negative half-life: 100 ps <<T, <10ms, - number of wire electrodes: 4-6, - number of wire electrodes d distance from grounded roll: 15 <d <30 mm.

Claims (1)

Procedure sets of different material quality components for each individual component! disposed by means of a device having an insulating substrate of a conveyor arranged beneath a feeding device, over a grounded conductive surface, spaced along electrically conductive electrodes at intervals of approximately 500 Hz, during the conveying path - preferably variable position - bulkhead two divided fogadó35 space is formed, characterized in that coupled to an alternating sign iinpulzusfcszültségct the electrodes, wherein the duration and amplitude of the opposite polarity half-cycles vary, preferably the first and second half period Tj and T ₂ duration The ratio of 40 is T, / T ₂ <0.5 and the ratio of the peaks with the opposite sign (U ⁺ or U ') is U ⁺ / U ~> 2, while the product of the voltage and time areas is the product of the opposite polarity T T f Udt; / Udt FIVE, 00 equals the mean electric field of the electrodes = 0.