Dielectric drying and heating assembly

The technology area

The invention relates to a dielectric drying assembly by means of electromagnetic energy -by dielectric heating.

The state of technology

The hitherto known assemblies to dry and heat the material are following: a) Driers utilizing warm or hot air

In the starting phase, drum, disk, cylindrical, belt, vibratory, stream, and fluid driers were integrated into production lines, with said driers having been developed for another purposes originally. In a working procedure, the suitability thereof to dry shavings turned out to be limited and the economic coefficients became worth as well. Therefore, to dry the shavings, special driers have been developed of which the rake driers and the pneumatic ones reached greatest spread recently. Rake driers

In these driers, a rotating system is made of radially located tubes which are heated by steam or water. On the outer periphery, blades are located in a form of spoons, with said blades lifting the shavings in a cylinder, letting them fall over the tubes and delivering them through the drier at the same time. The whole assembly works with natural air flow which leads off the evaporated humidity and drying proceeds mostly with contact heat transfer. To reach higher capacities, the drier is being delivered also as doubled one (two drum drier), i.e. there are two rotating systems located side by side in one solid covering with a diaphragm. As it followed from their performance, the conception thereof is suitable to dry loose substances and their economic operating parameters are very good, but frequent working failures are disadvantageous.

Stream and fluid driers

From stream driers the stream-and-slope combination drier with sorting effect on belts has been most widely spread.

Firstly, the fluid driers are destined do dry the woodworking industry waste (saw dust, shavings etc.), and with their pressure and velocity parameters of the drying environment, they are on the boundary of fluid and stream driers. Due to patented structural realization, the materials of various granulations and various specific mass can be dried continuously because

of being sorted and dried at the same time. The driers are made as single or double stage ones where the stages are ordered one above or behind the other. The two-stage drying improves the drying procedure with different size and mass of shavings which are carefully definitely dried, with small tolerance of the requested final humidity being kept. Jet driers

The assemblies of this type are characterized by high heat transfer efficiency due to intensive stirring and possible control of the material passage time through the drier. At present, they represent the final stage of drier development to dry the shavings. They have been spread in industrial plants mostly.

The drying environment is being led tangentially into a firmly located horizontal cylinder along its whole length by means of a jet at high velocity, with said cylinder being given a helical movement. In the jet, controlled guiding plates are installed by means of which different helical movement lead can be set due to which the drying time can be changed without changing the proper drying space length. The drier is provided with controlled recirculation of the drying environment. The dried material, led off by the drying environment, is being separated in a separator - a cyclone. As the drying environment, the oil or gas combustion products and air, heated in a calorifer, can be utilized, with said calorifer being steam-heated or hot- water-heated.

Evaluation of driers utilizing hot or warm air

From necessary costs comparison for individual drier types for 1 1 of dried shavings one can see that the jet and rake driers reach the most advantageous values; the belt driers prove least economical.

From the investment and depreciating costs as well as assembling and servicing expenses point of view with taking into consideration the working parameters as well as service life of individual drier types, the pneumatic, especially the jet driers prove most suitable to dry the shavings according to present state of engineering. Recently, this conclusion has been confirmed by that just the jet driers scored greatest spreading and application in production lines for wooden-shaving boards.

The humidity of wooden particles - cuttings, fibres, shavings, and saw dust etc. - entering into driers exceeds usually 30 per cent. They are dried usually to final humidity less man 10 per cent. The drying temperatures are limited by that self-ignition of wooden particles can

occur at temperatures above 180 ⁰ C approximately. Therefore, all driers are provided with an effective fire extinguisher. According to the drier type being used, the drying lasts in order of several seconds up to minutes. b) Driers using electromagnetic energy

Hitherto known methods to dry and heat the material:

- Drying and heating by means of a contact method - the material to be dried is inserted between heating plates and heating penetrates from surface into the material depth.

- The drying and heating by means of overheated and overdried air - the material is heated by over-dried and overheated air originated by energetic raw materials burning procedure.

- The drying and heating by means of an induction method - the material to be dried is interlaid with ferromagnetic inserts which are heated by an inductive solenoid, with the material to be dried being heated afterwards due to contact with said inserts.

- The drying and heating by means of microwave sources - by means of an magnetron type microwave source, working selectively at frequencies 2.45; 1.25; 0.85 and 0.5 GHz, with the whole material profile being heated in a resonance waveguide — a cavity.

Usually, the assemblys according to preceding points are completed by a device decreasing the atmospheric pressure in the drying and heating space.

The hitherto known assemblies to dry loose materials, especially organic ones, consist of a drying device, mostly consisting of a rotating drum or a belt provided with a material inlet and outlet as well as an inlet of a mixture of combustion products and air from a boiler. The saw dust, gas fissions or light fuel oil are used as fuel medium. These methods consume a plenty of energy. In burning the fuel medium, harmful stuffs are being released. As further disadvantage of mentioned solutions, dust particles escape during exhausting the originated vapour.

Except for above mentioned drying and heating by means of overheated and overdried air, other heating and drying methods cannot be utilized in a continuous process. The heating chamber must always be filled and emptied. In an assembly, using the electromagnetic energy as a source, there is a great danger of high energy electromagnetic waves leakage at a level harmful for human health.

The hitherto known assemblies for drying loose materials, especially for organic ones, consist of a drying device, mostly of a rotating drum or a belt provided with a material inlet and

outlet and with a supply of the mixture of combustion product and air from a boiler. As a fuel medium the saw dust, gas fissions or light fuel oil are being used. These methods consume a great deal of energy. With the fuel medium burning, harmful substances are released. Further disadvantage of mentioned solutions is based on dust particles escape during the originated vapour exhausting.

The nature of invention

The assembly according to the invention is closed in a protective chamber and connected to an electric energy source, and provided with an outlet of the processed material. The substance of the solution is based on that the assembly consists of a power oscillator which is connected to at least one application device by a HF line.

The application device is joined with the material outlet.

The power oscillator is a free oscillating solo-oscillator working at the frequency of 360 kHz up to 40 MHz. The power oscillator is water or air cooled.

The application device according to the proposed solution consists of at least two electrodes, with one of which being perforated, and contains a pneumatic device and a transport device.

The electrodes can be arranged one above the other as a parallel condenser or arranged one side by side as a planar condenser.

In front of the application device a preparatory device is inserted to let the material pass through the application device.

The assembly is controlled by a programmable automat and its energy output consists of a π- cell or a parallel coupling.

In an advantageous solution the transport device, the pneumatic device and the electrodes in the application device are mutually arranged so that the humid air is exhausted tangentially with respect to the material passage direction.

The material outlet consists of a stirring section or of a final drying section. The operating parameters and safety of the power oscillator and of the application device are governed by a programmable automat.

It is about a continuous drying and heating process utilizing the electromagnetic energy in the frequency range of 360 kHz to 40 MHz. A special transport device delivers the dried and heated material through a dielectric capacitive chamber in which the material is being heated dielectrically due to which the processed material humidity decreases. The whole process is

- S - governed by an automat in compliance with the requested outlet parameters - i.e. temperature, humidity, and amount of the dried material.

As opposed to similar and up to now used assemblies based on material hot-air-heating or drying, the combustion products, generated by burning of the fuel medium, are not used for material drying and therefore, no harmful substances escape. Further contribution for non- polluting the air is a principle of dried material movement in the application device, said movement being made by means of a transport device, and thanks to it no dust particles escape into the environment. The newly designed assembly dries the material with by far lower energy consumption.

List of the pictures on drawings

Fig. 1 presents a block diagram of the assembly.

On the Fig. 2 there is an oblique-angled view of the assembly, on the Fig. 2A ₅ there is an elevation of the assembly which is a variant of the parallel condenser.

The Fig. 3 presents an oblique-angled view of the assembly and on the Fig. 3 A, there is an elevation of the assembly as a variant of the planar condenser.

Examples of performing of the invention

Example 1

Dielectric drying and heating assembly, made according to the proposed solution, is closed in a protective cage 4. The assembly is connected to an electric energy source.

The outlet 9 of the processed material 8 forms a part of the protective cage 4 and the material

8 is then destined for further processing.

Inside the cage 4 there is a power oscillator 1 which is connected to the application device 3_ with a HF feed line 2. The HF feed line 2 is a coaxial or two-wire line, hi this case, the application device 3 consists of two electrodes 12 one of which is perforated.

In the application device 3 the electrodes V2 are arranged one above the other as a parallel condenser 6.

Further, the application device 3_ consists of a pneumatic device ϋ and of a transport device

10 and a belt for the batch process and is completed with filling and a discharging devices formed by a band or worm conveyer.

The transport device H), the pneumatic device H, and the electrodes V2 are mutually arranged so that the dried air is exhausted tangentially with respect to the direction of the material 8 passage.

In front of the application device 3 the preparatory device 23 is inserted for the passage of the material 8 through the application device 3. Further, the application device 3 is joined to the outlet 9 of the material 8. In compliance with the kind of material the outlet 9 of the material consists of a stirring or drying section.

The assembly is controlled by a programmable automat and its energy output is formed by a π-cell or by a parallel coupling.

The power oscillator I is a free oscillating single oscillator working at frequency of 3.5 MHz.

The operational parameters and security of the power oscillator I and of the application device 3_ are governed by a programmable automat.

Example 2

An assembly similar to that mentioned in the Example no. 1 has been made.

The HF line 2 is formed by a coaxial or a two-wire line.

In this case, the application device 3 consists of three electrodes Yl all of which are perforated.

In the application device 3 the electrodes 12 are arranged one besides the other as a planar condenser 7. The power oscillator i works at the frequency of 27 MHz.

Industrial usability

The proposed assembly can be utilized in a wood working, paper or furniture making industry. It can be utilized also in preparation of biomass for its further processing. The application is possible in other fields where the continuous heating and drying are necessary.