GB2438958A

GB2438958A - Radio frequency thermal treatment arrangement

Info

Publication number: GB2438958A
Application number: GB0710630A
Authority: GB
Inventors: Francesco Domenico De
Original assignee: G E A F Srl
Current assignee: G E A F Srl
Priority date: 2006-06-06
Filing date: 2007-06-04
Publication date: 2007-12-12
Anticipated expiration: 2027-06-04
Also published as: GB0710630D0; ITPR20060052A1; GB2438958B

Abstract

A system (1) for radio-frequency drying or pasteurization or sterilization, comprising a treatment chamber (2) with an electrode system therein, which is composed of an upper electrode (4) and a base electrode (5) and generates radio-frequencies in the range from 10 to 100 MHz; a capacitive system (18) which controls the power transmitted to such electrode (4) by a radio-frequency generator; the product to be treated being located between such electrodes (4, 5). The base electrode (5) includes a plate having telescopic guides (6), which acts as a pull-out carriage loaded with the products (7) to be treated. The base electrode may be adjustable in height by mechanism 14 and may be immersable in water 16 to cool products after treatment.

Description

* 2438958 SYSTEM FOR RADIO-FREQUENCY THERMAL DRYING,

PASTEURIZATION OR STERILIZATON TREATMENTS

DESCRIPTION

The present invention relates to a system for radio-frequency thermal treatments, which is particularly designed to meet two needs: * Low-temperature drying of food products, such as: fruit, vegetables, fresh filled pasta; to preserve color and taste while avoiding the classical damages caused by exposure to high temperatures.

* Applying possibly high-temperature treatments, such as pasteurization C-85-95 C) or sterilization C- 120-130 C), to food products, without affecting their organoleptjc properties and the appearance of packages.

Concerning the drying treatment, it is known that evaporation of a given substance is its change from the liquid to the vapor stage, which may occur at any temperature.

When a liquid is subjected to varying external pressure it evaporates at different temperatures.

One kilogram of pure water, which conventionally evaporates at 100 C at 1 atmosphere pressure (about 1 bar), can be also vaporized at about 80 C if pressure drops to 0.5 atmospheres.

The system of the invention heats the whole mass of a water-containing product, and evaporates water at about 60 C without using air flows.

A special stainless steel cylindrical chamber (treatment chamber), equipped with all required safety equipment, maintains pressure at the desired level throughout the process.

A vacuum generator pump is operated for a few minutes and, using special instruments, pressure in the treatment chamber is changed to about 0.3 -0.8 bar to depressurize the chamber.

Then, a radio-frequency generator is operated, which is designed to cause molecular agitation, thereby raising the temperature of water particles, which will evaporate at about 500 -70 C, depending on the depressurjzatjon induced.

The product so treated will have a less "baked" and oxidized appearance, after a less time-consuming process.

Concerning thermal treatments, it is also known that certain pasteurization and sterilization treatments can be applied after packaging to avoid later product contamination.

During thermal treatment, the volume of the food preparation in the package tends to increase, and to create such a pressure as to deform the container, especially when the latter is formed of a plastic material; also, if a closing plug is provided, the package may be opened.

To avoid the above drawbacks, radio-frequency heating systems are used in an environment in which pressure may be increased to oppose the pressure generated in the containers.

The system of this invention provides rapid heating of the whole mass of a food preparation in its container, by heating the product to pasteurization or sterilization temperatures in a short time.

A stainless steel cylindrical chamber (treatment chamber or autoclave), maintains pressure at the desired level throughout the process.

A compressor is operated for a few minutes and, using special instruments, pressure in the chamber is changed to max 3 -5 bar.

Then, the radio-frequency generator is operated, which is designed to cause molecular agitation, thereby raising the temperature of the product to be treated, to values in a range from 120 C to 130 C, depending on the applied pressure.

The product so treated will have a better, i.e. less "baked" and oxidized appearance.

The radio-frequency autoclave system fulfils two needs: > Low temperature drying of food products, such as fruit, vegetables, fresh and/or filled pasta; to preserve color and taste while avoiding the classical damages caused by exposure to high temperatures.

> Applying possibly high-temperature treatments, such as pasteurization C-85- 95 C) or sterilization (-120-130 c), to food products, without affecting their organoleptic properties and the appearance of packages.

These objects and advantages are achieved by the system for radio-frequency thermal drying, pasteurization or sterjljzaton treatments of this invention, which is characterized by the annexed claims.

These and other features will be more apparent from the following description of a few embodiments, which are shown by way of example and without limitation in the accompanying drawings, in which: -Figure 1 is a front view of a system for radio-frequency thermal drying, pasteurization or sterilization treatments, -Figure 2 is a side view of the system of Figure 1.

Referring to Figures 1 and 2, numeral 1 designates a system for radio-frequency thermal drying, pasteurization or sterilization treatments, which is comprised of a treatment chamber 2, i.e. a cylindrical autoclave, containing an electrode system in which radio-frequency electric fields are generated between a radio-frequency field emitting electrode 4 and a base or ground electrode 5, the latter being formed of a stainless steel sheet having telescopic guides 6, which acts as a pull-out carriage.

The electrode system is operated by a radio-frequency generator composed of an oscillator 41 and a power supply box 41 and high voltage controls, and in this example these units are located in a special cabinet 40.

In further detail, the tunnel, i.e. the autoclave 2 has a casing consisting of an electrowelded structure formed of stainless steel sheets and profiles.

Two perfectly hermetic loading and unloading doors 20, 21 are provided at its ends, which are formed of high frequency shielding mesh gaskets.

The doors are opened laterally and locked as follows: -the back door 21, only used for occasional maintenance, is locked by screws and bolts, -the front door 20, used for the process, is locked by a manual rack actuator having an electric limit stop which is designed to start the automatic cycle and control the pneumatic door-locking actuator.

The autoclave 2 has visual inspection windows 13 to illuminate or check the product, as well as a certain number of passages for the power supplies, probes, handling equipment, etc. The chamber 2 can withstand a positive pressure of 3-5 bar during overpressure operation, for pasteurization and sterilization treatments and a negative pressure of 0.3-0.8 bar during vacuum operation for low temperature drying treatments.

The chamber 2 is pressurized by compressed air from the mains or a compressor, which passes through a composite filter unit and is thereby de-oiled and filtered to remove impurities and foul smells, by passage through active carbons.

Then, using a pneumatically-controlled valve, the flow is metered to reach the pressure setpoint as

selected in operating specifications.

Vacuum is generated using a pump of suitable size.

A pneumatically controlled valve modulates air flow to the pump until it reaches the setpoint as

selected in the specification.

Referring to Figure 2, the ground electrode 5 includes a plate having telescopic guides 6, which acts as a pull-out carriage on which the products 7 to be treated are placed, and in this example the carriage, which slides within the guides, is led out of the chamber 2; the corresponding door 20 is shown with dashed lines as it is obviously open.

Above the ground electrode 5, the corresponding upper electrode 4 is height adjustable by means of a motor, for adjustment of the distance between the product 7 and the electrode 4: this distance is known in the art as "air gap".

The plate of the ground electrode 5 may be set at three different heights using a pantograph actuator 14, namely: -at the upper limit stop, corresponding to the radio-frequency treatment and/or heating position (as shown in Figure 1), -at an intermediate position, corresponding to the loading or unloading position with the pull-out carriage extracted (as shown in Figure 2), -at the lower limit stop, corresponding to the configuration in which the treated product 7 is cooled by being dipped in water 16; thus, the treatment chamber 2 will be partly filled with water, which is maintained at a low temperature by an internal radiator 8.

The water level is below the plate of the ground electrode 5 in the treatment configuration (upper limit stop).

All the movements of the ground electrode 5 are automatically controlled by a motor.

Photoelectric limit stop switches, not shown, may be installed on the motor pin for detecting the position of the lower ground electrode plate.

By adjusting the air gap between the radio-frequency field emitting electrode 4 and the ground

electrode 5, the radio-frequency electric field

strength may be optimized according to the product to be treated and to the degree of uniformity required by the process; the greater the distance, the more uniform the treatment and the lower processing time performance.

The whole structure of the radio-frequency field

emitting electrode 4 is supported by a frame of non-magnetic material and is borne by insulating columns of low dielectric loss material.

A potentiometer and two limit switches are installed on the motor pin to define the operating

position of the radio-frequency field emitting

electrode 4.

The radio-frequency generator has means for generating radio-frequency energy, such as an oscillator 41, a high-voltage power supply box 42 and power controls, as well as protection and power disconnecting elements.

In the illustrated example, the oscillator 4]. and all its auxiliary components are located above the autoclave 2, and are supported by an appropriate frame.

The triode is mounted in the oscillator 41 in a Class C oscillator configuration.

The resonant circuit applied thereto sets the oscillation frequency at the operating value, such as 27.12 MHz +1-0.6%.

By an inductive connection and a coaxial connection line 25, the radio-frequency energy is transferred from the generator to a capacitive power control system 18 for supplying power to the electrode plate in the treatment chamber 2.

The power supply box 42 and high voltage controls comprise a power disconnecting switch, i.e. a thermal-magnetic circuit breaker with a door locking system having the mains power connected thereto; the high voltage rectifier which is supplied with power by the power transformer-booster, constitutes the power supply that transforms the mains frequency three-phase voltage (400 VAC) into dc high voltage (8000 VDC) and provides the energy required for operation of the generator.

The power box further includes the components for automation, control and check of the various power supplies.

The system will obviously have a suitable automation and electric control panel 30 which contains the elements for controlling the operation of the machine, which are managed by a PLC.

The resonant circuit preferably sets the oscillation frequency at the operating value of 27.12 MHz or 13.56 MHz: the system may also obviously operate at frequencies from 10 to 100 MHz.

The system 1 is obviously equipped with the required cooling liquid inlet and outlet pipes 52, 53, a tap, not shown, for filling water 16, a manifold 100 for filling water 16, a discharge pipe 51 for discharging water 16, a manifold 54 for connection with the vacuum pump and a safety valve 55, a manifold 101 for compressed air.

The radio-frequency field emitting electrode 4 may

have various shapes, possibly three-dimensional shapes, including a cylindrical shape.

Claims

CLAIMS

1. A system (1) for radio-frequency thermal drying, pasteurization or sterilizaton treatments, characterized in that it comprises: a. a treatment chamber (2) containing b. an electrode system composed of a radio-

frequency field emitting electrode (4) and a

corresponding ground electrode (5), and generating an electric field at radio-frequencies in the range from to 100 MHz; c. a radio-frequency generator, generating frequencies in the range from 10 to 100 MHz; d. a capacitive system (18) which controls the power transmitted to said electrode (4) by the radio-frequency generator; the product to be treated being located between said electrodes (4, 5)
2. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that said ground electrode (5) includes a plate having telescopic guides (6), which acts as a pull-out carriage, and said plate is loaded with the products (7) to be treated.

3. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that a compressed air mains or a compressor is connected to said treatment chamber (2) for generating in said chamber (2) an overpressure to 3 -5 bar for pasteurization and sterilization treatments.

4. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that a pump is connected to said treatment chamber (2) for generating in said chamber (2) a negative pressure to 0.3 -0.8 bar for low-temperature drying treatments.

5. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that said radio-frequency field emitting electrode (4) is height adjustable by means of a motor, for adjustment of the distance from the product (7), i.e. the ground electrode (5).

6. A system (1) for radio-frequency thermal 2.0 treatments as claimed in claim 2, characterized in that the plate of the base electrode (5) has a pantograph actuator (14) which places it at various heights, according to the process stages, i.e. radio-frequency treatment, extraction of the telescopic carriage or cooling of the treated product.

7. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that the treatment chamber (2) has two doors (20, 21) at its ends, for inspection, loading and unloading; said doors (20, 21) being perfectly hermetic.

8. A system (1) for radio-frequency thermal treatments as claimed in claim 7, characterized in that the tightness of the doors (20, 21) is obtained using high frequency shielding wire gaskets.

9. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that the back door (21) is opened laterally and is locked using screws and bolts, whereas the front door (20) is locked by a manual rack actuator with an electric limit switch.

10. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that the radio-frequency generator has means for generating radio-frequency energy, such as an oscillator (41), a high-voltage power supply box (42) and power controls, as well as protection and power disconnecting elements.

11. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that said treatment chamber (2) is partly filled with water maintained at low temperature by an internal radiator (8), the water level being below the position of the plate of the base electrode (5) during treatment.

12. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that the resonant circuit of the generator sets the oscillation frequency in the range of ISM (Industrial, Scientific and Medical) frequencies, particularly at 27.12 14Hz.

13. A system (1) for radio-frequency thermal treatments as claimed in claim 1, characterized in that said radio-frequency field emitting electrode (4) may have various shapes, possibly three- dimensional shapes, including a cylindrical shape.