A DRYER FOR FREE-FLOWING DIELECTRIC MATERIALS Field of the Invention

This invention relates to equipment for drying free-flowing dielectric materials in a microwave field and may be practiced in the chemical industry, pharmaceutical industry, food industry, and agriculture.

Increase in equipment productive capacity while ensuring a high quality of a dried-up material and decrease in an energy intensity of a drying process in one of the requirements for devices for drying free-flowing dielectric materials in a microwave field. Description of the Prior Art

Known in the prior art is a dryer for free-flowing dielectric materials [Russian Patent No. 2152571 , Int. Cl. F26 B11/04, 3/347] comprising a horizontal chamber supported rotatably in two bearings fixed at covers in lateral openings of drum; heating elements made in the form of a system of slotted-guide resonant radiators and connected to a microwave oscillator; a device for feeding a heated air to the chamber internal cavity; and a moisture discharge device. In this dryer, the waveguide extends into the internal cavity of the metal drum through an opening provided in the fixed cover of one of the drum lateral openings and a heated air feed channel provided with a perforated shield and a wet air discharge channel extend through openings in the fixed cover of the other drum lateral opening. The slotted-guide resonant radiator system is turned by an angle between 40° and 45° with respect to a dryer base and provided with quarter-wave reflectors.

This prior art dryer only enables up 50 kg in weight of a free-flowing material to be dried-up. If a product charge increases, a non-uniform distribution of microwave energy occurs, in particular, because of energy absorption by the surface layer.

Known in the prior is also a dryer for free-flowing materials [Russian Patent No. 2230270, Int. Cl. F26 B11/06, 3/347] comprising, to ensure microwave energy distribution uniformity in the product volume in the event of a great charge of a drum, the drum rigidly mounted in a metal cylindrical casing supported rotatably in two sliding bearings installed in fixed covers in lateral openings of the casing, the casing comprising a surface wave transmission line made in the form of a ribbed structure on an internal cylindrical surface which surface comprises alternate concentric grooves of (0.04 to 0.05)λ wide and ribs of (0.02 to 0.03)λ thick, the cylindrical walls of the drum being perforated and made of a radio transparent material, a microwave energy being

applied to the surface wave transmission line from a separate microwave oscillator whose frequency differs from that of a microwave oscillator connected to a slotted- guide resonant radiator system.

A disadvantage of this prior art device is a design and operation complexity attributed, in particular, to the utilization of two microwave oscillators and, accordingly, necessity in coordinated actions in controlling the oscillators. It is rather difficult to ensure a stable operation of two magnetrons connected to a common load. Magnetron crosstalk would result in decrease in magnetron efficiency and, possibly, in suppression of oscillation. Furthermore, the disadvantages of these dryers include a low efficiency of utilizing a microwave energy because of such a design provides for microwave energy application perpendicularly to a product layer this resulting in the occurrence of a standing wave with a ratio of more than 2 in a microwave oscillator - waveguide line - muitimode resonator system. In addition, the material drying process is performed at an atmospheric pressure and, to remove moisture out of the material being dried, the latter should be heated to high temperatures. In doing so, some elements may be decomposed and undesired compounds may be formed this resulting in the loss of quality of finished products or even in the impossibility of drying certain materials.

Known in the prior is also a dryer for free-flowing dielectric materials [Ukrainian Patent No. 76014, Int. Cl. F26B 17/30] comprising a muitimode resonator chamber made of two truncated cones of different heights and a cylindrical section which connects the cones to each other at their larger bases, the height ratio of the higher truncated cone to the cylindrical section to the lower truncated cone of the resonator being 2:1:0.5. The higher truncated cone is connected by its mouth flange via a vacuum-tight flange to a microwave energy waveguide input. The muitimode resonator chamber is supported rotatably by means of a rotation device, as well as movably vertically due to its support at uprights having curved sections which sections form an angle of 15° to 20° with a device base as does so the axis of the microwave energy waveguide input. A dielectric duct used for pumping out the chamber volume extends from a chamber bottom edge along its axis. An air blowdown device is disposed coaxially with said duct on the outside of the chamber, is connected permanently thereto and is connected to the rotation device of the chamber.

The disadvantages of this dryer which lower both drying quality and microwave energy utilization efficiency include, in particular, the design of chamber

volume blowdown and pumping out units. The design of these units contributes to the adherence of small particles of material to the rotational joint to the microwave energy waveguide input, the occurrence of a sintered product crust, and, therefore, deterioration in microwave radiation passage into the chamber. Ukrainian Patent Application No. 2007 00677 filed on 22.01.2007 and entitled

"A Device for Drying Free-Flowing Dielectric Materials", the Applicants being ZAT Technological Park Single Crystals, DNU NTK Single Crystals Institute of the National Academy of Science of Ukraine, teaches that both high drying quality and decrease in process energy intensity are ensured by a dryer which comprises a multimode resonator chamber supported rotatably and movably vertically at uprights and is made of two truncated cones of different heights and a cylindrical section which connects the cones to each other at their larger bases. The chamber shape is determined by the height ratio of the higher truncated cone to the cylindrical section to the lower truncated cone of the resonator being 2.5:1:0.25, an angle between the axis and generatrix of the higher cone being between 20° and 21°. The higher truncated cone is connected by its mouth flange via a rotational joint to a microwave energy waveguide input. The axis of the microwave energy waveguide input and, thus, the longitudinal axis of the chamber form an angle between 20° and 21° with a horizontal base of the device. A dielectric duct used for pumping out the chamber volume extends from a chamber bottom edge along its axis through a rotational vacuum seal near the bottom plane, is bent upwards relative to the horizontal base of the device, and is provided with a filter head to prevent the product from entering it. A chamber blowdown device disposed coaxially with said duct on the outside of the chamber comprises an air duct extending into the chamber near the chamber mouth flange plane and is provided, at its end, with a sprayer.

Such a configuration ensures a high quality of drying where a multimode resonator chamber volume is not more than 50 liters. If a product volume being dried simultaneously and, thus, a multimode resonator chamber volume are to be increased, both shape and design of the multimode resonator chamber, the design of the microwave energy input unit, the slope of the chamber in its operational position relative to the horizontal base of the dryer, the designs of the chamber volume pumping out and blowdown devices do not ensure the desired drying quality. Low operational properties make such a design unsuitable for use for this purpose.

Based on the aggregate of substantial features, we have selected the latter of the above analogs as the prototype. Disclosure of the Invention

The present invention has as its object to develop a high efficient dryer for drying simultaneously a significant volume of a free-flowing dielectric material, that is to say, a dryer which is characterized by a high productive capacity and high microwave energy utilization efficiency at the same time.

The object of the invention is achieved in that the prior art dryer for free- flowing dielectric materials comprising a multimode resonator chamber supported rotatably at uprights by means of a rotation device and made of two truncated cones of different heights and a cylindrical section which connects the cones to each other at their larger bases, a rotational vacuum tight joint to a microwave energy waveguide input, a chamber blowdown device with an air duct, and a chamber volume pumping out device with a dielectric duct extending from a chamber bottom edge along its axis through a rotational vacuum seal near the bottom plane and bent upwards relative to the horizontal base of the dryer, in accordance with the invention, includes a horn antenna disposed between the rotational vacuum seal and the higher truncated cone the horn of which antenna being closed, at the output, by a radio transparent partition with a through hole in its center; contactless position pickups disposed at uprights near the horn antenna; the chamber being supported at the uprights at an angle between 8° and 10° with the horizontal base. Furthermore, the cylindrical section of the chamber is provided with a charging-discharging hatch having a cover and a vacuum and microwave seal. The height ratio of the higher truncated cone to the cylindrical section to the lower truncated cone of the resonator is 0.75:1 :0.5 and an angle between the axis and generatrix of the higher truncated cone being between 8° and 10°. The air duct of the chamber blowdown device extends into a horn cavity of the horn antenna near the radio transparent partition plane. In order to improve operational properties of the device in accordance with the invention, to enable a drying process to be monitored, strain gages are installed at uprights, temperature sensors are provided at the interior surface of the chamber; the chamber volume pumping out device includes a pressure meter, an air filter, and a second pressure meter disposed in series in a vacuum pipe.

A rotatable support of the chamber, the installation of the contactless position pickups at the uprights, and the provision of the charging-discharging hatch at the

cylindrical section of the chamber, which hatch is closed tightly by the cover, enable raw stock to be charged in a convenient manner and a dried-up product to be discharged completely if the chamber is positioned as desired. In addition, the chamber shape determined by the height ratio of chamber components and by the angle between the axis and generatrix of the higher cone also facilitates the complete product flowing out during its discharge. It is just the resonator chamber shape with the predetermined ratio of parameters in accordance with the invention combined with the predetermined chamber slope at an angle between 8° and 10° with the horizontal base of the drier and with the provision of the microwave energy input unit comprising the horn antenna disposed between the rotational vacuum-tight joint and the higher truncated cone that ensures a substantially full absorption of microwave energy, the temperature pattern uniformity throughout the volume of material being dried and, thus, a high efficiency of drying process and a high quality of a dried-up product. Chamber rotation also assists to the establishment of uniform temperature throughout the volume of material. In addition, the configuration of the chamber blowdown device in accordance with the invention with the air duct extending into the horn cavity of the horn antenna near the plane of the radio transparent partition, which is disposed at the horn output and has the through hole in its center, combined with the chamber volume pumping out device with the dielectric duct extending from the chamber bottom edge along its axis through the rotational vacuum seal near the bottom plane and bent upwards relative to the horizontal base of the dryer, ensures the desired drying process conditions in terms of predetermined temperature and pressure and prevents condensate from being formed at, and small particles from being adhered to, the surface of the radio transparent partition thereby improving both microwave energy utilization efficiency and dried-up material quality. The strain gages installed at the uprights and the temperature sensors provided at the interior surface of the chamber enable an online drying process monitoring. The provision of the chamber volume pumping out device with the pressure meter, the air filter, and the second pressure meter disposed in series in the vacuum pipe also ensures a process parameter monitoring. It will be thus appreciated that if a significant volume of material is dried simultaneously, there should be no deviation from the process parameters. The vacuum and microwave seal of the charging-discharging hatch ensures chamber tightness when the charging-discharging hatch cover is closed.

Brief Description of the Drawings

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:- Fig. 1 is a schematic view of a dryer for free-flowing dielectric materials in accordance with the invention.

Referring now to Fig. 1 , the drier in accordance with the invention comprises a multimode resonator chamber made of a higher truncated cone 1 , a lower truncated cone 2 connected to each other at their larger bases by a cylindrical section 3. The height ratio of the higher truncated cone 1 , the cylindrical section 3 and the 2 is 0.75:1 :0.5 and an angle between the axis and generatrix of the higher truncated cone 1 is between 8° and 10°. Provided at the cylindrical section 3 of the multimode resonator chamber is a charging-discharging hatch 4 with a cover 5 used to charge and discharge a material 6 to be dried. The charging-discharging hatch 4 has a vacuum and microwave seal 7.

The higher truncated cone 1 is connected, at its smaller base, to a horn of a cylindrical horn antenna 8, which horn is closed by a radio transparent partition 9 with a through hole 10 in its center. The horn antenna 8 is connected through a rotational microwave joint 11 by a microwave input 12 to a microwave oscillator (not shown). The multimode resonator chamber is supported reversibly rotatably at uprights 13 so that its longitudinal axis forms an angle between 8° and 10° with a horizontal base 14. A geared motor for rotation is not shown in Fig. 1.

Disposed on the outside of the multimode resonator chamber is a chamber blowdown device with a blower to feed a blowdown gas (not shown) and an air duct 15 extending into the horn cavity of the horn antenna near the radio transparent partition 9 plane.

To pump out the chamber volume through a rotational vacuum joint 16 at a bottom 17, a stationary dielectric duct 18 extends along the chamber axis near the bottom 17 plane. The dielectric duct 18 is connected by a flexible vacuum pipe 19 to a vacuum pipe (not shown). In the vacuum pipe 19, a pressure meter 20, an air filter 21 , and a second pressure meter 22 are disposed in series.

Contactless position pickups 23 are disposed at the uprights 13 near the horn antenna 8. Disposed at the uprights 13 are also strain gages 24; temperature sensors

25 are provided at the interior surfaces of the higher truncated cone 1 , the lower truncated cone 3 and the cylindrical sections 2 of the multimode resonator chamber.

Industrial Applicability

The dryer in accordance with the invention operates as follows: The multimode resonator chamber supported at the uprights 13 so that its longitudinal axis forms an angle between 8° and 10° with the horizontal base 14 is positioned using the contactless position pickups 23 disposed at the uprights 13 and the geared motor for rotation so that it is convenient to charge the material 6 through an open charging-discharging hatch 4 having the vacuum and microwave seal 7. The material 6 is charged and the cover 5 is closed tightly. The vacuum pump is turned on and the multimode resonator chamber is pumped out through the vacuum pipe 19 and the dielectric duct 18 till the desired pressure. The geared motor for rotation is also turned on and the multimode resonator chamber starts rotating. The rotational vacuum joint 16 at the bottom 17 rotates together with the multimode resonator chamber while the dielectric duct 18 remains immovable. When the chamber pressure reaches <10 mm Hg, the blower to supply and control the blowdown gas is turned on while the volume is continued to be pumped out. The blowdown gas is fed to the multimode resonator chamber through the air duct 15 extending into the horn cavity of the horn antenna 8 near the radio transparent partition 9 plane and through the through hole 10 in the center of 9 until it reaches a prebreakdown pressure. In doing so, the multimode resonator chamber is blown down and small particles of raw stock are blown off the radio transparent partition 9 plane of the horn antenna 8.

The microwave oscillator is then turned on. The microwave oscillator irradiates energy and, through the microwave input 12, the rotational microwave joint 11 , and the horn antenna 8, exposes the material 6 to a microwave impact. In the dryer in accordance with the invention, the rotation axis of the multimode resonator chamber forms an angle between 8° and 10° with the horizontal base 14 so that, during the rotation of the multimode resonator chamber, the material 6 gets mixed up retaining at all times the shape of a wedge the vertex whereof is oriented towards the microwave oscillator this facilitating material 6 heating uniformity 6, while the dielectric duct 18 will always be above the level of the material 6 enabling the chamber volume to be pumped out.

In the process of operation, material heating uniformity is monitored by means of the temperature sensors 25; the material weight is monitored by means of the strain

δ gages 24 disposed at the uprights 13. The chamber pressure as well as the contamination degree of the air filter 21 is monitored by means of the pressure meters 20 and 22 disposed in the vacuum pipe 19.

The dried up material 6 is discharged as follows: The microwave oscillator and the vacuum pump are turned. off. Using the contactless position pickups 23 and the geared motor for rotation, the multimode resonator chamber is positioned so that it is convenient to discharge the material 6 through the charging-discharging hatch 4.

The blowdown gas is fed by the blower to the multimode resonator chamber through the air duct 15 till an atmospheric pressure. The cover 5 of the charging-discharging hatch 4 is opened to discharge the dried-up material to special reservoirs.