GB2057655A - Methods of and devices for drying loose materials - Google Patents

Abstract

A method of drying a loose material comprises exciting vibrations in the material (2), sustained by mechanical impulses which also initiate single compression waves in the material (2), and removal of moisture therefrom. A device for carrying out the method comprises a drying chamber (1) provided with a vibration generating mechanism (3) made up of electromagnetic eddy- current inductors (10) coupled to a power supply (4) via switches, a discharge electrical energy accumulator (13), and elements (14) made of a highly conducting material. The drying chamber (1) also incorporates a moisture removal system 5, 7, 8 using compressed air. <IMAGE>

Description

SPECIFICATION Improvements in or relating to methods of and devices for drying loose materials The present invention relates to techniques of drying solid materials by removing moisture therefrom, and more particularly to a method of and a device for drying a loose material.

Such a method and device may be used in the production of chemicals, in the food industry, and in construction.

According to one aspect of the invention, there is provided a method of drying a loose material, comprising exciting vibrations in the material, sustained by mechanical impulses also initiating single compression waves in the material, and removing the surface moisture.

The material is preferably acted upon by electromagnetic field pulses.

Preferably, the material is acted upon simultaneously by at least one group of single electromagnetic field pulses.

Preferably the material is acted upon by mechanical pulses in mutually perpendicular directions.

Preferably, the duration of a single electromagnetic field pulse is between 10-5 and 10-2 sec, and the ratio of an interval between single electromagnetic field pulses to the duration of a single electromagnetic field pulse is from 10 to 10,000.

According to another aspect of the invention, there is provided a device for drying a loose material by the method according to invention, comprising a drying chamber provided with a vibration generating mechanism made up of electromagnetic eddy-current inductors coupled to a power supply via switches controlled by a programmable switching device and a discharge electrical energy accumulator, elements made of a highly conductive material arranged in direct proximity to the electromagnetic eddy-current inductors, and a surface moisture removal system.

Preferably, at least two adjacent electromagnetic eddy-current inductors are connected in series and form a coherent source of mechanical impulses, connected via a switch to the discharge electric energy accumulator.

Each switch preferably comprises a thyristor whose control gate is connected to the programmable switching device.

Each element made of a highly conducting material may comprise a plate inserted between an electromagnetic eddy-current inductor and a wall of the drying chamber.

Preferably, the electromagnetic eddy-current inductors are arranged on mutually perpendicular walls of the drying chamber.

It is thus possible for the process of drying loose materials to be sped up and made more efficient.

It is also possible to minimize the power consumed from an external source, owing to its being stored in the discharge electrical energy accumulator at intervals between mechanical impulses to provide for a subsequent impulse action.

The power N, of mechanical impulses is determined from the formula: t+T N,=Nz 21 t t where N2 is the power of the external power supply; '1 is the efficiency of the device; t is the duration of a single electromagnetic field pulse; T is an interval between single electromagnetic field pulses, and T 10 < 410,000.

t Then, at a single electromagnetic field pulse duration of, for example, 1 1 10-3, the interval between pulses is 1 sec, the efficiency of the device is 90%, and the power of the power supply is 900 times less than that of the mechanical impulses.

The invention will be further described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a general view of a device for drying a loose material, with electric circuitry providing for individual activation of the vibration generating mechanisms, constituting a preferred embodiment of the invention; Figure 2 represents an electric circuit diagram of a device for drying a loose material, whose circuitry provides for simultaneous activation of the vibration generation mechanisms integrated into coherent sources of mechanical impulses, constituting another preferred embodiment of the invention; and Figure 3 shows an arrangement of the electromagnetic eddy-current inductors with respect to the drying chamber of part of yet another preferred embodiment of the invention.

A preferred method of drying a loose material resides in excitation of vibrations in the material and removal of the surface moisture, the vibrations being sustained by mechanical impulses which also initiate single compression waves in the material.

Therewith, the mechanical impulses speed up the drying process and enhances its efficiency. In the preferred method, the mechanical impulses are provided by an electromagnetic field.

The use of-single electromagnetic field pulses substantially intensifies their action. In an alternative embodiment, the material is acted upon simultaneously by at least one group of single electromagnetic field pulses.

The synchronous application of a group of single electromagnetic field pulses permits extending the area of simultaneous action of single compression waves on the loose material, thereby improving the drying efficiency.

In the preferred method, further speeding up of the drying process and removal of a greater amount of moisture from a loose material are achieved by applying mechanical impulses thereto in mutually perpendicular directions. In this case, the mechanical impulses may be applied simultaneously in two mutually perpendicular directions or in series.

The duration of a single electromagnetic field pulse ranges from 1 0-5 to 1 0-2 sec, which is adequate for efficient drying of loose materials.

The amplitude of mechanical impulses depends on the electrnmagneti field pulse duration and increases as the latter becomes shorter. At a single electromagnetic field pulse duration above 10-2 sec, the efficiency of drying a loose material sharply decreases because the amplitude of mechanical impulses in this case is insufficient for creating the acceleration of the material particles necessary to displace them, compact the material, and remove moisture therefrom.

At a single electromagnetic field pulse duration below 10-5 sec, technical difficulties arise. The amplitude of mechanical impulses will exceed the value at which stresses appear in the loose material drying device, equal to the fatigue or cyclic strength limit of the material of which the latter is made.

The ratio of an interval between single electromagnetic field pulses, during which power from an external source is stored, to the duration of a single electromagnetic field pulse varies from 10 to 10,000 and is optimum from the viewpoint of minimizing power consumption from the external source. A ratio higher than 10,000 will make the loose material drying time too long. A ratio lower than 10 will result in a higher power consumption because the electrical energy accumulator will have to be charged to the rated value within a shorter period of time.

EXAMPLE Sand was dried by the above method. To determine the efficiency and parameters of the drying process, a known amount of water had been added to a known amount of sand.

The sand was dried by exciting vibrations therein and removing the surface moisture, the vibrations being sustained by mechanical pulses which also initiated single compression waves in the sand.

The mechanical impulse action was provided by single electromagnetic field pulses.

The drying chamber was filled with 10 kg of dry sand and 2 kg of water. Applied to its bottom and two opposite walls were simultaneously 60 pulses of an electromagnetic field having an energy of about 20 J. The duration of each single pulse was 10-3 sec, while each interval between single pulses was 1.5 sec. The sand drying process took 1.5 min.

The supplied power was 0.2 kW. The released water was removed after the drying was over.

After drying, the sand weighed 10.85 kg, i.e. it lost 57.5% of the added water. Thus, the method permits speeding up of the drying process and enhancing of its efficiency, and minimizes the power consumption from an external source.

Referring now to Figure 1, a device for drying a loose material by the preferred method comprises a drying chamber 1 with a loose material 2, provided with a vibration generating mechanism 3 arranged in immediate proximity thereto and coupled to a power supply 4, as well as a surface moisture removal system including, for example, nozzles 5 mounted on a wall 6 of the drying chamber 1 and associated with a source 7 of compressed air. The moisture removal system also includes a pipe 8 arranged on a wall 9 of the drying chamber 1 opposite to the wall 6. The vibration generating mechanism 3 is made up of electromagnetic eddy-current inductors 10 (four in this embodiment) connected via switches controlled by a programmable switching device 11 to the power supply 4.The switches are essentially thyristors 12 whose control gates are connected to the programmable switching device 11. The mechanism 3 also comprises a discharge electrical energy accumulator 13 and elements 14 made as plates of a highly conductive material, such as copper or aluminum. The elements 14 are arranged between a wall 15 of the drying chamber 1 and the respective electromagnetic eddy-current inductors 10, in direct proximity to both.

If the walls 6, 9 and 1 5 of the drying chamber 1 are made of a highly conductive material, the elements 14 are not necessary.

Each electromagnetic eddy-current inductor 10 comprises a few coils of wire enclosed in a case of a dielectric material.

The discharge electrical energy accumulator comprises a capacitor 1 6 and a means 1 7 for charging it, made, for example, as a step-up transformer 18 whose primary winding is connected to the power supply 4, and a rectifier 19 connected to the secondary winding of the transformer 18. The programmable switching device 11 comprises a series circuit including a pulse generator 20, a ring shift register 21 and a pulse amplifier 22.

Figure 2 shows an embodiment of the electric circuitry of the device, wherein every two adjacent electromagnetic eddy-current inductors 10 are placed in series and form a coherent source 23 of mechanical impulses, coupled to the discharge electrical energy accumulator 11 via a thyristor 12.

In various embodiments of the device, the number of coherent sources 23 of mechanical impulses and electromagnetic eddy-current inductors 10 may vary.

Shown in Figure 3 is an embodiment in which the electromagnetic eddy-current inductors 10 are secured to mutually perpendicular walls 6, 1 5 and 9, 1 5 of the drying chamber 1 with the aid of brackets 24. Each electromagnetic eddy-current inductor 10 is attached to its bracket 24 with the aid of leads 25 of the inductor 10. To eliminate losses of the electromagnetic field appearing around each electromagnetic eddy-current inductor 10 as a current pulse passes therethrough, the brackets 24 should preferably be made of a dielectric material.

The device for drying a loose material operates as follows.

When the discharge electrical energy accumulator 13 (Figure 1) is energized from the power supply 4, the capacitor 16 charges through the step-up transformer 1 8 and rectifier 1 9. When a signal is applied from the programmable switching device 11 to the control gate of one of the thyristors 12, the latter is turned on, and the capacitor 1 6 discharges into the electromagnetic eddy-current inductor 10 associated with the thyristor 12. A current discharge pulse passes through the coils of the electromagnetic eddycurrent inductor 10 and initiates an electromagnetic field pulse which induces secondary pulse current in the corresponding element 14 made of a highly conducting material.

Interaction of the current discharge pulse passing through the electromagnetic eddy-current inductor 10 with the pulse current induced in the element 14 results in an abrupt repulsion of the element 14 together w;th the wall of the drying chamber 1 from the electromagnetic eddy-current inductor 10. The resulting mechanical impulses act upon the wallow the drying chamber 1, causing elastic deformation therein. Therewith, the amplitude of an impulse should not exceed the value at which stresses in the structure of the drying chamber 1 reach the fatigue limit. Single compression waves start propagating from the points of excitation of the elastic deformation in the wall of the drying chamber 1 into the loose material 2, displacing its particles.Periodic action of single compression waves on the loose material 2 results in its compaction, and the moisture contained therein is forced out on its surface. The surface moisture can be removed from the drying chamber 1 through the pipe 8, for example, with the aid of compressed air supplied into the drying chamber 1 through the nozzles 5 from the source 7.

Such moisture removal may be performed several times in the course of drying the loose material 2, as it is accumulated on the surface, or once at the end of drying.

To extend the area of action of mechanical impulses on the drying chamber 1, use is made of a plurality of electromagnetic eddy-current inductors 1 0. In this embodiment, four inductors 10 connected to the power supply 4 are employed. The programmable switching device 11 controls activation of the inductors 10 in a particular sequence. The pulse generator 20 produces a continuous train of pulses which are applied to the ring shift register 21 and amplified by the amplifier 22.

Prior to operation, the first digit place of the register 21 contains unity. The rest of the places contain noughts, and as the first pulse from the generator 20 is applied, the thyristor 12 associated with the first digit of the shift register 21- is turned on transferring the unity to the second place. The arrival of the second pulse from thegenerator 20 turns on the thyristor 1 2 associated with the second place of the shift register 21, and the unity passes on to the next place. Thus, each time a subsequent pulse is applied from the generator 20, it turns on the thyristor 12 associated with that place of the shift register 21, which contains unity.

A thyristor 1 2 being turned on discharges the capacitor 16 into the electromagnetic eddycurrent inductor 10 connected to that particular thyristor 12, thereby producing mechanical impulses acting on the loose material 2 near the inductor 10 in question.

The device operates in a pulsed mode. When a thyristor 12 is turned on, a current discharge pulse from the capacitor 1 6 initiates a single electromagnetic field pulse around the inductor 10, whose duration is from 1-0-5 to 10-2 sec. Then follows an interval during which the electrical energy from the power supply 4 is accumulated to subsequently produce the next electromagnetic field pulse. Such operation provides for a mechanical impulse power far exceeding the supplied power.

For simultaneous activation of several electromagnetic eddy-current inductors 10 (Figure 2), the latter are integrated into coherent sources 23 of mechanical impulses, controlled by a single thyristor 1 2.

Synchronous activation of several electromagnetic eddy-current inductors 10 brings about an interference of elastic deformations in the wall of the drying chamber with the result that the area of simultaneous action of single compression waves on the loose material 2 is extended and the drying efficiency is improved.

In this case, the device operates similarly as described above except that a thyristor 12 being on discharges the capacitor 16 into several, e.g.

two, electromagnetic eddy-current inductors 10 integrated into the coherent source 23 of mechanical impulses, at a time.

To enhance the drying efficiency, the electromagnetic eddy-current inductors 10 (Figure 3) should preferably be arranged on mutually perpendicular walls 6, 1 5 and 9, 15 of the drying chamber 1. The sequence of operation of the inductors 10 may be different. For example, the electromagnetic eddy-current inductors 10 mounted on all walls 6, 9 and 1 5 of the drying chamber 1 may operate simultaneously or successively. It is also possible that the inductors 10 on the walls 6 and 9 are first to operate simultaneously, then those mounted on the wall 15, or in any other sequence. All these possibilities are equivalent as far as the efficiency and consumption of the supplied power are concerned.

Thus, it is possible to speed up the drying process, enhance its efficiency and minimize the power consumed from an external source. The use of structurally simple components and the absence of moving parts in the device provided for its long service life.

Claims (12)

1. A method of drying a loose material, comprising exciting vibrations in the material, sustained by mechanical impulses also initiating single compression waves in the material, and removing the surface moisture.

2. A method as claimed in Claim 1, wherein the material is acted upon by single electromagnetic field pulses.

3. A method as claimed in Claims 1 or 2, wherein the material is acted upon simultaneously by at least a group of single electromagnetic field pulses.

4. A method as claimed in any one of Claims 1 to 3, wherein the material is acted upon by mechanical pulses in mutually perpendicular directions.

5. A method as claimed in any one of Claims 2 to 4, wherein the duration of a single electromagnetic field pulse is between 10-5 and 10-2 sec, and the ratio of an interval between single electromagnetic field pulses to the duration of a single electromagnetic field pulse is from 10 to 10,000.

6. A device for drying a loose material by the method of Claim 1, comprising a drying chamber provided with a vibration generating mechanism made up of electromagnetic eddy-current inductors coupled to a power supply via switches controlled by a programmable switching device and a discharge electrical energy accumulator, elements made of a highly conductive material arranged in direct proximity to the electromagnetic eddy-current inductors, and a surface moisture removal system.

7. A device as claimed in Claim 6, wherein at least two adjacent electromagnetic eddy-current inductors are connected in series and form a coherent source of mechanical pulses connected via a switch to the discharge electrical energy accumulator.

8. A device as claimed in Claim 6 or 7, wherein each switch comprises a thyristor whose control gate is connected to the programmable switching device.

9. A device as claimed in any one of Claims 6 to 8, wherein each element made of a highly conducting material comprises a plate inserted between a respective electromagnetic eddycurrent inductor and a wall of the drying chamber.

10. A device as claimed in any one of Claims 6 to 9, wherein the electromagnetic eddy-current inductors are arranged on mutually perpendicular walls of the drying chamber.

11. A method of drying a loose material, substantially as described hereinabove.

12. A device for drying a loose material, substantially as described hereinabove with reference to and as illustrated in the accompanying drawings.