IT202200026736A1 - Dehumidification Apparatus and Method - Google Patents

Description

Description of industrial invention

Dehumidification Apparatus and Method

Background of the invention

[0001] The invention relates to a method and/or a dehumidification apparatus, in particular for the dehumidification of loose material, i.e. material in the form of particles such as, for example, granules and/or micro-granules and/or pellets and/or powder and/or flakes or the like. The invention in question may be suitable, in particular, for reducing the moisture content in particles of plastic material.

[0002] Specifically, but not exclusively, the invention can be applied in the context of a plant for the treatment of incoherent plastic material, such as, for example, a plant for the dehumidification and/or drying and/or crystallization and/or packaging and/or transport in vacuum and/or under pressure of the incoherent plastic material. Such plant can be intended, in particular, to feed a user machine, such as, for example, a machine for processing and transforming plastic materials, in particular an extruder that supplies the extruded material to an injection and/or blow molding and/or compression molding apparatus.

[0003] In the field of transformation of plastics into a finished product, it is known to dehumidify the plastic material in particulate form (polymer granules) before subjecting it to the extrusion and moulding process, to ensure the quality of the moulded product, in particular for plastics with high hygroscopic properties, for example those based on polyethylene terephthalate (PET), polyamide (PA), polycarbonate (PC), or some copolymers such as acrylonitrile butadiene styrene (ABS). Typically, the polymer granule is dried and/or dehumidified in a hopper into which a continuous flow of hot, dry and/or dehumidified air is introduced. The polymer granule that exits the hopper dried and/or dehumidified can be brought to the molten or semi-molten state, for example to be extruded and injected into a mould.

[0004] The prior art teaches how to dehumidify incoherent plastic material by irradiation with radio frequency waves or microwaves.

[0005] US Patent Publication 5,420,404 shows the use of radio frequency waves to dehumidify dielectric material, such as hygroscopic plastic resins in pellet form, by heating the material in a continuous process inside a container in which the material descends by gravity and is passed through by a flow of preheated air.

[0006] US Patent Publication 2008/0060212 A1 shows a process for drying plastic granules by microwave irradiation inside a hopper where the granules are conveyed by gravity.

[0007] However, the drying and/or dehumidification processes of the polymer granule of the prior art can be improved in several respects.

[0008] First, it is desirable to stabilize and standardize the conditions of the polymeric material exiting the hopper dried and/or dehumidified, so that these conditions (in particular, temperature and humidity) are those desired for the entire mass of the polymeric material. This is complicated by various factors, for example by the considerable mass of the material to be heated, or by the thermal gradient that is generated in the hopper between the surface and the core of the granule.

[0009] Secondly, it is desirable to reduce energy consumption, evenly distribute heating energy throughout the mass of the material, increase productivity and reduce the duration of the dehumidification process.

Summary of the invention

[0010] An aim of the invention is to provide a solution, alternative to those of the known art, for dehumidifying incoherent plastic material by using radio frequency waves.

[0011] An aim of the invention is to propose a suitable solution to overcome one or more of the aforementioned limitations and drawbacks of the known art.

[0012] One advantage is to homogenize the temperature of the plastic granule so as to reduce the thermal gradient between the surface and the core of the granule.

[0013] One advantage is to homogenize the humidity of the plastic granule so as to reduce the humidity gradient between the surface and the core of the granule.

[0014] One advantage is to stabilize and standardize the conditions (particularly temperature and humidity) of the processed material.

[0015] One advantage is to homogenize the desired conditions (in particular, temperature and humidity) throughout the entire mass of the processed material.

[0016] Other advantages are reducing energy consumption and/or distributing heating energy evenly throughout the material mass and/or increasing productivity and/or decreasing the duration of the dehumidification process.

[0017] These purposes and advantages, and others, are achieved by an apparatus and/or a system and/or a method according to one or more of the claims listed below.

[0018] In one example, a dehumidifying apparatus comprises at least one container for loose material, at least one duct with at least one opening for introducing a process gas into the loose material in the container, and a heating device with at least one electrode connected to a radio frequency generator, wherein the electrode and a portion of the duct are arranged at a distance from each other and wherein the electrode is surrounded by (and in contact with) the loose material and the portion of the duct is also surrounded by (and in contact with) the loose material. The electrode may, in particular, be a rod-shaped element, i.e. an element with one dimension (length) greater than the other two.

[0019] In one example, a method of drying particulate solid material comprises the steps of feeding the material into a container where the material moves from an upper region of the container to a lower region of the container, heating the material in the container by generating an oscillating magnetic field with radio frequency waves that strike the material in the container (with the effect, in particular, of also supplying energy to the core of each particle, heating the entire particle from the core to the surface and resulting in transferring moisture from the core to the surface of the particle) with a frequency of between 300 KHz and 300 GHz (more specifically with a frequency of between 1 Mhz and 1 Ghz, or between 1 Mhz and 100 Mhz, or between 10 Mhz and 100 Mhz, or between 1 Mhz and 50 Mhz, even more specifically with a frequency of between 10 Mhz and 50 Mhz), and to invest the material in the container with a flow of process gas (with the effect of evacuating the moisture transferred to the surface), in particular with a process gas (e.g. air) previously heated and/or dehumidified.

[0020] The oscillating radio frequency magnetic field can be generated, in particular, by using at least one electrode that is immersed and surrounded by (and in contact with) the material contained in the container (in particular with a bar-shaped electrode arranged in a decentralized manner with respect to a central axis of the container) so that a part of the material is interposed between the electrode and a central area of the container (in particular, a central area where at least a portion of a process gas transport duct is arranged) and another part of the material is interposed between the electrode and a peripheral area of the container.

[0021] The process gas may be supplied by at least one conduit (which is not configured to contain, in use, the material) configured to transport the process gas and comprising (in particular, at a lower outlet end of the conduit) at least one opening for introducing the process gas into the container (in a process volume defined by at least one wall of the container and capable of being filled with the material to be processed). The gas inlet opening is arranged, in particular, in a non-peripheral area of the container (for example, in a central area of the container or in any case in an area closer to the centre of the container than the position of the electrode).

[0022] The duct may comprise at least one duct portion (which does not contain the material) arranged within the container so that it can be surrounded by (and be in contact with) the material in the container. The gas transport duct is configured so that the flow of process gas along the duct portion is directed from top to bottom until it reaches the opening through which the process gas contacts the material in the process volume. The gas inlet opening (an opening comprising, for example, a diffuser cone) may be arranged, in particular, at a lower end of the duct portion.

[0023] The conduit portion may be arranged, in particular, adjacent to the electrode and at a certain distance from the electrode, such that the space inside the container between the conduit portion and the electrode is, in use, occupied by a portion of the material. A distance (e.g. the minimum distance) between the electrode and the conduit portion may be between one-eighth and one-quarter of the internal transverse dimension of the container (internal diameter for a cylindrical container) at the height of the container at which this distance is measured. The conduit portion may be arranged, in particular, in a central vertical area inside the container. The longitudinal axis of the conduit portion and the longitudinal axis of the electrode may be arranged parallel to each other, for example in a vertical direction.

[0024] The electrode is connected to a radio frequency generator which can be adjusted in power and/or frequency (in particular by means of electronic and programmable control means) based on one or more characteristics of the material, in particular based on the chemical composition. The radio frequency generator can be connected to a number N of electrodes, where N can be between 1 and 7 (1 ? N ? 7. It is possible, however, to provide for the use of a number of electrodes N > 7, for example 7 < N ? 13, or even N > 13.

[0025] Each electrode may be in the form of a rod. Each rod may be extended in length with a longitudinal axis arranged vertically. The electrodes may be, in particular, parallel to each other, with a circumferential arrangement. The electrodes may be, in particular, angularly equidistant from each other around a vertical axis of the container (dehumidification hopper). This vertical axis of the container may, in particular, pass through a lower outlet of the container through which the material exits the process volume. The construction material of the electrodes may comprise, in particular, at least one metallic material such as, for example, copper, aluminium, brass, special alloys, or even a combination of the aforementioned materials. The construction material of the duct portion may comprise, in particular, an electrically conductive material, or in any case a non-dielectric material (for example metallic material).

[0026] Each electrode may comprise, or may be provided with, or may be operatively associated with, at least one temperature sensor, configured in particular to detect a surface temperature of the sensor.

[0027] The length of the electrode bars (each with a vertically arranged longitudinal axis) can be chosen according to the geometry of the container. The length of the electrode bars (each with a vertically arranged longitudinal axis) can be chosen according to the type of material being processed (for example, the nature or chemical composition of the plastic resin). It is possible to use bars of different lengths (for example, depending on the geometry of the container or the type of material being processed). In particular, it is possible to use a different length for each bar, or to use two or more groups of bars in which each group of bars comprises two or more bars of the same length and the length of each group of bars is different from the length of the other group of bars or of the other groups of bars.

[0028] The solid particulate material being processed may include, in particular, plastic material (polymer resin in granular form). The processed plastic material may include one or more polymer resins included in the following set: polyethylene terephthalate (PET), polyamide (PA), acrylonitrile butadiene styrene (ABS), polyparaphenylene sulfide (PPS), polystyrene (PS), polyvinyl chloride (PVC), polysulfone (PSU), polymethyl methacrylate (PMMA). Furthermore, the processed plastic material may include, in particular, post-consumer recycled plastic (PCR).

[0029] The radio frequency generator can be configured, in particular, to emit radiation with a frequency between 300 KHz and 300 GHz. More specifically, the radio frequency generator can be configured to emit radiation with a frequency between 1 MHz and 1 GHz (i.e. 10<6 >? 10<9 >Hz), or between 1 MHz and 100 MHz, or between 10 MHz and 100 MHz, or between 1 MHz and 50 MHz, or more specifically between 10 MHz and 50 MHz). In a practical, non-limiting example, a generator selectively configurable at 13.56 MHz or 27.12 MHz has been used, although other frequencies can also be used.

[0030] Each electrode bar can have a different shape and size depending on the geometry of the container (dehumidification hopper) and/or depending on the process volume defined by the container.

[0031] Each electrode may be controlled (by programmable electronic control means including, for example, a central processing unit, a programmable logic controller, a microprocessor, etc.) with a set point value of the power supplied to the electrode. Each electrode may be controlled with a maximum threshold value, which must not be exceeded, of the electrode surface temperature. Each electrode may be controlled with a set point value of the electrode surface temperature. Control of each electrode achieves a desired transfer of radio frequency energy to the solid polymer resin particles. Power may be supplied to the electrode continuously, or as pulse trains to avoid localized overheating and/or plasticization of the material.

[0032] In particular, it is possible to provide that each bar is immersed in the material for most of its length or for its entire length, to improve the effectiveness of heating the material with the power emitted by the radio frequency. The number of electrodes (bars) can be chosen based on the volume of material to be treated and in which the electrodes themselves are immersed. The arrangement, number and shape of the electrodes can be chosen, in particular, in such a way as to reduce dead zones, i.e. the areas of the process volume (i.e. the internal volume of the container to which the material is fed) not affected by the radio frequency, and at the same time in such a way as to avoid areas of excessive overlapping of the radiation emitted by the electrodes, to avoid accumulations of energy with the risk of degradation of the material.

[0033] The process gas flow can be countercurrent to the descending flow (by gravity) of the particulate solid material. The process gas can include dried air and/or dehumidified air and/or an inert gas (nitrogen or nitrogen mixtures) or other suitable gas to reduce thermo-oxidative phenomena.

[0034] The process gas can be introduced into the process volume, in particular into the mass of material contained in the container (hopper), via a diffuser (e.g. a diffuser cone) arranged in a lower area of the container (in particular a central area) and spaced from a wall of the container which surrounds the diffuser and which defines the process volume.

[0035] Heating by the combined action of radio frequency and process gas (in particular, process gas preheated to a temperature higher than 50 °C, or higher than 60 °C, higher than 70 °C, or higher than 80 °C) allows, compared to heating with a single technology, to reduce energy consumption, to reduce treatment time, to increase the efficiency of moisture extraction.

[0036] The radio frequency generator can be controlled, in particular, based on the chemical-physical characteristics of the processed material and the process gas used (for example, based on the dielectric constant of the non-homogeneous mixture of processed material and process gas, which can be determined, for example, by means of the Maxwell Garnett equation). For example, in the case of PET processed with air, it is possible to generate waves with a radio frequency between 1 MHz and 100 MHz, or between 10 MHz and 50 MHz, for example equal to 27.12 MHz.

[0037] The radio frequency generator can be controlled, in particular, on the basis of a container filling factor, i.e. a ratio between the volume actually occupied by the material in the container during the process (a volume which can be controlled by known control means) and the maximum total volume available inside the container to contain the material itself.

[0038] It has been found that radio frequency increases its heating efficiency in the core of the pellet if the pellet has been preheated to a temperature higher than room temperature, for example if a PET pellet has reached a temperature above 70 °C. An increase in the temperature of the process gas has also been found in the vicinity of the radio frequency emitting electrode.

[0039] In one example, a dehumidification method comprises a first stage, wherein the particulate material is heated in a first container (up to a certain temperature) by a flow of process gas, and a second stage, wherein the material, taken from the first container and introduced into a second container, is further heated by radio frequency waves and a flow of process gas inside the second container.

[0040] The above two-stage drying method (with radio frequency heating in the second stage) can be used, in particular, for recycled polymer material (PCR plastic) or other material that may suffer high temperature treatment for a long time.

[0041] The above two-stage method with radio frequency heating in the second stage can be used, in particular, to process the material at a relatively low temperature in the first stage (in particular, with a process gas at a temperature below the degradation temperature of the polymer, e.g. below 65 °C for polyolefins and below 120-140 °C for PTE), achieving a more attenuated level of drying, and using radio frequency in the second stage for more intense heating down to the core of the plastic granule.

[0042] As previously mentioned, it has been found that radiofrequency heating of polymer granules allows for a significant speeding up of the extraction of humidity from the granule if the granule itself is already at a high temperature (in particular, by means of a preheating phase carried out in a first container placed upstream of the second container where the radiofrequency heating takes place), for example for PA and PET at a temperature between 100 °C and 140 °C. In this case, the evaporation efficiency and, therefore, dehumidification of the granule becomes much higher than with heating with process gas.

[0043] It has also been found that dehumidification by radio frequency heating is particularly effective when the loose material to be processed has a high degree of humidity, i.e. radio frequency heating may be more effective than heating with a process gas when the polymer granule has a high degree of humidity.

[0044] In one example, a dehumidification method comprises a first stage, in which the particulate material is heated in a first container by radio frequency waves and is passed through by a flow of process gas, and a second stage, in which the already at least partially dehumidified material, taken from the first container and introduced into a second container, is further dehumidified by a flow of process gas inside the second container.

[0045] The above two-stage dehumidification method (with radio frequency heating in the first stage) can be used, in particular, for polymeric material to be processed which presents high humidity.

[0046] It is therefore possible to envisage at least two examples of two-stage methods: a first example in which a radio frequency stage (with a process gas flow) precedes a non-radio frequency stage (with a process gas flow); a second example in which a radio frequency stage (with a process gas flow) follows a non-radio frequency stage (with a process gas flow).

[0047] ? a reduction (between 30% and 50%) in the dehumidification treatment time of the polymer resin was found for both the first and second example compared to a single-stage treatment.

[0048] It is possible to envisage a dehumidification method similar to the two-stage method mentioned above (a stage without radio frequency before or after a stage with radio frequency), but in this case carried out inside the same container (dehumidification hopper) with a single passage of material.

[0049] For this purpose, a single container can include in its process volume two process zones, similar to two stages as described above, by means of a particular shape and arrangement or configuration of the electrodes, so as to perform differentiated RF radio frequency heating in two or more zones at different heights of the process volume.

[0050] In particular, it is possible to activate RF heating only in an upper zone of the process volume, while the process gas flow passes through both the lower and upper zones of the process volume, resulting in a process similar to a two-stage process with a first stage in the upper zone with RF and a second stage in the lower zone without RF).

[0051] Alternatively, it is possible to activate RF heating only in a lower zone of the process volume, while the process gas flow passes through both the lower and upper zones of the process volume, resulting in a process similar to a two-stage process with a first stage in the upper zone without RF and a second stage in the lower zone with RF.

[0052] The material, which is loaded from above, first passes through the upper zone of the process volume. If the material is very moist, it can be dehumidified more efficiently in the upper zone by the RF heating, or if it is less moist, it can be preheated in the upper zone by the process gas flow.

[0053] The process with two process zones in a single container can be carried out, for example, by means of electrodes of relatively short length (or by electrodes of relatively long length but configured to operate under control only in a small, selectable portion of their length) so that the radio frequency emission is arranged, optionally, in an upper zone of the process volume or in a lower zone of the process volume, whereby it can be considered that there is a radio frequency stage arranged in the zone of the process volume where the electrodes operate and a non-radio frequency stage arranged in the zone of the process volume where the electrodes do not operate.

[0054] The arrangement of two process zones inside a single container allows for the execution of a process similar to a two-stage process also due to the fact that the material descends at a speed of descent inside a container with a known geometry and with a specific passage section of the material, in which the passage section can, in particular, be variable by proceeding from top to bottom and the descent speed of the material can, in particular, also be variable inside the container.

[0055] In general, the number N of electrodes for radio frequency emission can depend on the transverse dimensions of the container (hopper diameter) where the dehumidification process takes place, to ensure a homogeneous distribution of the energy provided by the radio frequency waves.

[0056] Each electrode may be oblong in shape (e.g., rod-shaped) arranged with a longitudinal axis parallel to an axis (usually vertical) of a material discharge opening at the bottom of the container. Each electrode may be attached to a lid that closes at the top a process volume defined by the container and may be arranged entirely beneath the lid.

[0057] Each electrode may be oblong in shape with a right cross-section having a maximum dimension of between 5 mm (millimeters) and 200 mm, in particular between 10 mm and 150 mm. This maximum dimension may be chosen according to the power of the radio frequency to be emitted. In particular, each electrode may comprise a cylindrical bar with a diameter of between 5 mm and 200 mm, or between 5 mm and 150 mm, or between 10 mm and 200 mm, or between 10 mm and 150 mm, or between 10 mm and 60 mm.

[0058] Each electrode may be equipped, in particular, with a temperature sensor, suitable in particular for detecting the surface temperature of the sensor. Such a sensor may comprise, in particular, a fibre optic sensor or another type of sensor configured in such a way as not to be affected by the action of the electromagnetic field generated by the radio frequency generator.

[0059] In one example, a material handling device may be provided in the container, for example by means of an agitator that mixes the material in the process volume and/or by means of a recirculation system that takes a part of the material from an outlet of the container and reintroduces it into an inlet of the container. The movement of the material in the container promotes a uniform diffusion of energy, improving the effectiveness of heating and dehumidification of the material. The handling device allows to increase the efficiency of the treatment, especially in the case of a batch-type process, which is particularly suitable above all for materials that require, due to their chemical-physical-mechanical characteristics, to be subjected to moderate temperature gradients or to be processed with reduced volumes of material to limit the thrust of the mass of the material on the discharge mouth of the container.

Brief description of the drawings

[0060] The invention may be better understood and implemented with reference to the attached drawings which illustrate some exemplary and non-limiting forms of implementation, in which:

- Figure 1 is a vertical elevation diagram of a first example of a dehumidifying apparatus for incoherent plastic material, with a radio frequency electrode, made in accordance with the present invention;

- figure 2 is a section of the dehumidification apparatus of figure 1 according to a horizontal section plane;

- Figure 3 is a vertical elevation diagram of a second example of a dehumidification apparatus for incoherent plastic material, with two radio frequency electrodes, made in accordance with the present invention;

- figure 4 is a section, according to a horizontal section plane, of the container of the dehumidification apparatus of figure 3;

- Figure 5 is a perspective view, sectioned along a vertical section plane, of a third example of a dehumidification apparatus made in accordance with the present invention, with three radio frequency electrodes;

- figure 6 shows a part of the apparatus of figure 5 which includes the electrodes for the application of energy with radiofrequency waves;

- figure 7 shows the apparatus of figure 5 not sectioned;

- Figure 8 is a vertical elevational section of a fourth example of a dehumidifying apparatus constructed in accordance with the present invention;

- figure 9 is a perspective view, sectioned along a vertical section plane, of the dehumidification apparatus of figure 8;

- Figures 10 and 11 show two examples of double-stage dehumidification systems made in accordance with the present invention.

Detailed description

[0061] For simplicity of explanation, similar elements of different embodiments have been indicated with the same numbering.

[0062] With reference to the above figures, the reference numeral 1 generally indicates a dehumidifying apparatus which can be used, in particular, to dehumidify incoherent plastic material, i.e. material in the form of particles such as, for example, granules and/or micro-granules and/or powder and/or flakes or the like. The dehumidifying apparatus 1 may be suitable, in particular, to reduce the quantity of humidity present in a granular plastic material intended, in particular, to feed a user machine 2, such as, for example, a machine for processing and transforming plastic materials, in particular an extruder which supplies the extruded material to an injection and/or blow moulding and/or compression moulding apparatus.

[0063] The dehumidification apparatus 1 comprises at least one container 3 that defines a process volume configured to contain the incoherent plastic material. The container 3 may comprise, in particular, a dehumidification hopper. The container 3 may comprise, in particular, at least one containment wall W that delimits the process volume. The containment wall W may comprise, in particular, at least one cylindrical wall portion with a vertical axis and at least one truncated conical lower portion. The containment wall W may be made, as in these examples, of electrically conductive material or in any case of non-dielectric material, in particular of metallic material such as, for example, steel, or stainless steel, or special alloys suitable for contact with plastic materials such as PET, PA, ABS, PPS, PS, PVC, PSU, PMMA, PCR, etc.

[0064] The container 3 may comprise, in particular, at least one material inlet 4 arranged above and at least one material outlet 5 arranged below. The container 3 may be configured, in particular, to allow a continuous flow of incoherent plastic material (in particular, a descent of the material by gravity) from the material inlet 4 to the material outlet 5. The container 3 may comprise, in particular, a vertical axis passing through the material outlet 5. The container 3 may be provided, in particular, with a feed hopper H arranged above the container 3 to feed the material to the material inlet 4 through which the material enters the process volume.

[0065] The dehumidification apparatus 1 comprises at least one conduit configured for transporting a process gas to the loose material to be processed (before the process gas comes into contact with the loose material to be processed in the process volume). The container 3 may comprise, in particular, at least one conduit inlet 6 through which the gas transport conduit may enter the container 3.

[0066] The gas transport duct may comprise, in particular, at least one opening 7 for introducing the process gas into the process volume. The opening 7 may comprise, in particular, a diffuser for the process gas (for example, a diffuser cone). The process gas is transported along the duct and then exits the duct through the opening 7 and thus comes into contact with the loose material contained in the process volume in the container 3. The duct comprises at least one portion of duct 8 arranged inside the container 3 in such a way as to be able to be immersed and surrounded all around by the loose plastic material that fills the process volume.

[0067] The duct portion 8 may be arranged, in particular, in a central vertical zone within the container 3. The opening 7 may be arranged, in particular, at a lower end of the duct portion 8. The duct portion 8 is configured, in particular, so as to transport a flow of process gas in a direction from top to bottom. The process gas transport duct is configured, in particular, so that the process gas flows in the duct portion 8 with a flow directed from top to bottom until it reaches the opening 7. The duct portion 8 may be, as in these examples, made of electrically conductive material or in any case of non-dielectric material (for example in metallic material, in particular steel, or stainless steel, or special alloys suitable for contact with plastic materials such as PET, PA, ABS, PPS, PS, PVC, PSU, PMMA, PCR, etc.). The portion of the duct 8 can be made, in particular, of the same material as the container 3.

[0068] The container 3 comprises at least one gas outlet T through which the process gas which has processed the loose material can escape. The gas outlet T can be arranged, in particular, in an upper region of the process volume.

[0069] It is possible to foresee, as in the specific example of figures 5-7, that the containment wall W is impermeable to the incoherent material and permeable to the process gas (in particular, the containment wall W could be perforated). The containment wall W internally delimits an interspace to allow a flow of the process gas. The container 3 may comprise, in particular, a peripheral wall P impermeable to the process gas. The peripheral wall P may perform, in particular, an external insulation function. The wall P may comprise, in particular, an insulation layer.

[0070] It is possible to foresee, as in the example of figures 8-9, an intermediate wall Y which is placed between the peripheral wall P and the containment wall W and which externally delimits the cavity through which the process gas flow passes. The intermediate wall Y can be arranged so as to at least partially surround the containment wall W and so as to define at least one annular cavity in which the process gas can pass.

[0071] In use, a portion of the process gas may exit the process volume through the containment wall W to enter the annular cavity, with the possibility of returning to the process volume by passing again through the containment wall W, and then exiting through the gas outlet T.

[0072] The dehumidifying apparatus 1 comprises a heating device with at least one radio frequency generator 9 and with at least one electrode 10 connected to the radio frequency generator 9.

[0073] The electrode 10 is arranged inside the container 3 at a distance D from the portion of the duct 8 and in such a way that it can be surrounded all around by the incoherent plastic material that fills the process volume.

[0074] The attached figures show three dehumidification apparatuses which have been represented, purely by way of example, with one electrode 10 (figures 1-2), with two electrodes 10 (figures 3-4) and with three electrodes (figures 5-7 and figures 8-9), even if the number N of electrodes may be different for each of the apparatuses shown (for example, N = 1, or N = 2, or N = 3, or N = 4, or N = 5, or N = 6, or N = 7, or N > 7, for each of the dehumidification apparatuses described with reference to figures 1-9).

[0075] Each electrode 10 may be arranged, in particular, at a higher level than the opening 7. Each electrode 10 may be arranged, in particular, next to the portion of the duct 8. Each electrode 10 may comprise, in particular, at least one portion of the electrode next to the portion of the duct 8 and shaped and arranged in such a way that each section or segment or point of the portion of the electrode located at a certain vertical level corresponds to a section or segment or point of the portion of the duct 8 located at the same vertical level. Each electrode 10 may be, in particular, interposed between the portion of the duct 8 and the containment wall W of the container 3. Each electrode 10 may be fixed to a cover K which closes the process volume at the top. Each electrode 10 may descend from the cover K downwards.

[0076] Each electrode 10 may be arranged, in particular, in the container 3 in such a way that a part of the process volume, which may be filled with the incoherent plastic material, is interposed between the electrode 10 and the conduit portion 8. Each electrode 10 may be arranged, in particular, in the container 3 in such a way that another part of the process volume, which may be filled with the incoherent plastic material, is interposed between the electrode 10 and the containment wall W.

[0077] Each electrode 10 may, in particular, be oblong in shape. Each electrode 10 may, in particular, be extended along a longitudinal axis. The duct portion 8 may, in particular, extend along a duct axis parallel to the longitudinal axis. The longitudinal axis may, in particular, be arranged vertically. Each electrode 10 may, in particular, comprise at least one section orthogonal to the longitudinal axis with a maximum transverse dimension of between 10 mm and 60 mm. The duct portion 8, spaced from the electrode 10, may perform a function as a ground electrode. A distance D (minimum distance) between each electrode 10 and the duct portion 8 may, in particular, be between one eighth and one quarter of the internal diameter of the container 3.

[0078] The heating device may comprise, in particular, two or more electrodes 10 each of which is arranged in the container 3 in such a way that it can be surrounded by the incoherent plastic material that fills the process volume. The aforementioned two or more electrodes 10 may be arranged, in particular, in a circumferential manner around the duct portion 8. The aforementioned two or more electrodes 10 may be arranged, in particular, around a vertical duct axis of the duct portion 8 angularly spaced from each other.

[0079] The aforementioned two or more electrodes 10 may be configured, in particular, so that an area occupied by the aforementioned two or more electrodes 10 in a horizontal cross-section of the process volume is included in a range of 1% to 6% of a total area of the horizontal cross-section of the process volume, where total area means the area that can be occupied by the incoherent plastic material, thus excluding at least an area occupied by the portion of the duct 8 itself. The aforementioned two or more electrodes 10 may be configured, in particular, so as to have at least one dimension different from each other, in particular a dimension (length) considered along a downward direction (substantially vertical direction) of the incoherent plastic material.

[0080] The material inlet 4 may be arranged, in particular, at a higher level than the opening 7. The material inlet 4 may be arranged, in particular, at a higher level than the entire portion of the duct 8. The material inlet 4 may be arranged, in particular, at a higher level than the entire electrode or at least a part of the electrode. The material outlet 5 may be arranged, in particular, at a lower level than the opening 7. The material outlet 5 may be arranged, in particular, at a lower level than the entire portion of the duct 8. The material outlet 5 may be arranged, in particular, at a lower level than the entire electrode 10. The vertical axis of the container 3 may be, in particular, coaxial with the duct axis of the duct portion 8.

[0081] The process gas may be fed to the process volume 3 in a closed loop or in an open loop. The dehumidification apparatus 1 may comprise a treatment system 11 configured to treat the exhausted process gas exiting the process volume to generate fresh process gas and then to feed the fresh process gas obtained from the treatment system 11 back into the process volume in a closed loop. The treatment system 11 may comprise, in particular, at least one actuator 12 (e.g., a fan) to generate a flow of process gas in the closed loop. The treatment system 11 may comprise, in particular, a dehumidifying device 13 (e.g., of the molecular sieve type, in particular with a double molecular sieve tower) to dehumidify the process gas before it enters the process volume.

[0082] The treatment system 11 may comprise, in particular, a decontaminating device 14 to reduce the content of unwanted volatile substances present in the process gas exiting the process volume. The decontaminating device 14 may comprise, in particular, a condensation system configured to condense certain substances (e.g., volatile organic components) contained in the process gas and to evacuate the condensed liquid that has formed. The decontaminating device 14 may comprise, in particular, an activated carbon filtration system configured to retain certain volatile substances (e.g., volatile components not retained by the condensation system) contained in the process gas.

[0083] In particular, it is possible to provide a monitoring system 15 that measures the content of one or more undesirable substances (e.g. total organic carbon) in the process gas upstream and/or downstream of the decontaminating device 14. The monitoring system 15 can be used, in particular, for the feedback control of one or more process parameters (e.g. one or more process parameters suitable for increasing or decreasing the condensing power of the condensing system) based on the measured values. The decontaminating device 14 can comprise both the condensing system and the activated carbon filtration system, for example arranged in series one after the other.

[0084] The dehumidifying apparatus 1 may comprise, in particular, at least one thermostatically controlled heater (not shown, e.g. a known type heater) configured to heat the process gas so that it enters the container 3 at a desired temperature (above ambient temperature). The process gas heater may be arranged, in particular, between the dehumidifying device 13 and the duct inlet 6.

[0085] The dehumidification apparatus 1 may comprise, in particular, programmable electronic control means, connected to the sensors and actuators of the apparatus and configured to control the dehumidification process.

[0086] Figures 10 and 11 schematically show two systems for dehumidifying incoherent plastic material. Each system comprises at least one dehumidifying stage with RF radio frequency and at least one dehumidifying stage with PG process gas connected to each other by an in-line (in particular, continuous) feeding system for the incoherent plastic material.

[0087] The RF dehumidifying stage may comprise, in particular, a dehumidifying apparatus configured to perform radio frequency heating of the particulate solid material combined with a process gas treatment (in particular, previously heated and dehumidified process gas) passing through the material, e.g. an apparatus such as one of those described above with reference to Figures 1 to 9.

[0088] The process gas dehumidification stage PG may comprise, in particular, a dehumidification apparatus configured to perform a treatment with process gas (previously heated and dehumidified) which passes through the particulate solid material contained in a hopper (without providing for heating of the particulate solid material with radio frequency).

[0089] The dehumidification stage with process gas PG may comprise, in particular, a dehumidification apparatus, such as one of those described above, but without the radio frequency heating device, or provided with the radio frequency heating device which, however, is not activated.

[0090] The PG process gas dehumidification stage can be arranged, in particular, so as to process the incoherent plastic material before the RF dehumidification stage (as in the example of Figure 10), or after the RF dehumidification stage (as in the example of Figure 11).

[0091] In the examples of Figures 1-9, each electrode 10 extends in length approximately to the lower end of the duct portion 8, in proximity to the diffuser which has the opening 7, with an extension approximately equal to the height of the cylindrical portion of the container 3. It is possible to envisage other examples in which each electrode has a more limited extension and is arranged only in an upper zone of the process volume, or only in a lower zone of the process volume, forming a dehumidifying zone with RF radio frequency only in the upper zone or only in the lower zone of the process volume, thus allowing a sort of two-stage process within the same container. It is possible to envisage examples with one or more ?short? electrodes arranged only in the upper zone of the process volume and one or more ?short? electrodes arranged only in the lower zone of the process volume, selectively operable to generate RF only in the upper zone, or only in the lower zone, or in both zones. Examples can be envisaged with one or more ?long? electrodes extending into both the upper and lower zones of the process volume and one or more ?short? electrodes arranged only in the upper zone of the process volume and/or one or more ?short? electrodes arranged only in the lower zone of the process volume, selectively operable to generate RF of greater or lesser magnitude in the upper zone and/or in the lower zone. Examples can be envisaged with one or more ?long? electrodes each divided into two or more electrode portions selectively operable to generate RF of different magnitude in different zones of the process volume.

[0092] A dehumidification method is provided which can be implemented, in particular, by using a dehumidification apparatus or a dehumidification system as described above.

[0093] The method comprises the step of introducing incoherent plastic material to be dehumidified into a process volume defined by a container 3. The method comprises the step of introducing a process gas into the process volume through at least one opening 7 of at least one conduit for transporting the process gas. The conduit comprises at least one conduit portion 8 which is arranged inside the container and which is surrounded all around by the incoherent plastic material filling the process volume. The method comprises the step of emitting radio frequency waves by means of at least one electrode 10 arranged inside the container 3 at a distance D from the conduit portion 8. The electrode 10 is surrounded all around by the incoherent plastic material filling the process volume.

[0094] The method may comprise, in particular (see figure 10), before the step of introducing the incoherent plastic material into the container 3, a preliminary step of heating and dehumidifying the incoherent plastic material, in the dehumidifying stage with process gas PG which precedes the dehumidifying stage with RF radio frequency. This preliminary step may be carried out, in particular, inside a dehumidification hopper using a process gas. The method may comprise, in particular, a transfer step in which the processed material exiting the dehumidification hopper of the dehumidifying stage with process gas PG is transferred in line into the process volume of the dehumidifying stage with RF radio frequency. In this case the incoherent plastic material may comprise, in particular, recycled polymeric material PCR, or other polymeric material which does not tolerate high temperatures for a long time.

[0095] The method may comprise, in particular (see figure 11) a transfer stage in which the processed material exiting the process volume of the RF dehumidifying stage is transferred to a dehumidifying hopper of the PG process gas dehumidifying stage where the loose plastic material is dehumidified by a process gas. In this case the loose plastic material to be processed (first in the RF stage and then in the non-RF stage) may comprise, in particular, material which has a relatively high moisture content, so that the RF heating, which occurs in the first stage, is particularly effective without running the risk of damaging the material.

[0096] The method may comprise, in particular, a step of controlling the emission of the radio frequency waves, in particular by controlling the radio frequency generator 9, based on one or more chemical-physical characteristics of the incoherent plastic material and/or the process gas. The method may comprise, in particular, a step of controlling at least one characteristic of the process gas (e.g., flow rate and/or temperature and/or moisture content) based on one or more chemical-physical characteristics of the incoherent plastic material and/or the process gas.

[0097] The above one or more chemical-physical characteristics - on the basis of which the emission of radio frequency waves can be controlled and/or on the basis of which at least one characteristic of the process gas can be controlled - may be selected, in particular, within a set of characteristics which includes: (1) a dielectric constant of a mixture of incoherent plastic material and process gas and/or (2) a filling factor (i.e. a ratio between a volume actually occupied by the incoherent plastic material in the container and a total volume available in the container to contain the incoherent plastic material), and/or (3) a temperature of the incoherent plastic material or a temperature of the process gas and/or (4) a parameter indicative of the moisture content in the incoherent plastic material or a parameter indicative of the moisture content in the process gas and/or (5) a chemical composition of the incoherent plastic material.

[0098] In particular, the radio frequency generator 9 can be controlled by the electronic control means (in power and/or frequency) based on the dielectric constant of the used mixture of incoherent plastic material and process gas. The radio frequency generator 9 can be controlled by the electronic control means (in power and/or frequency) based on the aforementioned filling factor. The radio frequency generator 9 can be controlled by the electronic control means (in power and/or frequency) based on the chemical composition of the incoherent plastic material.

Claims (18)

1. Dehumidification apparatus (1), comprising: - at least one container (3) that defines a process volume configured to contain inconsistent plastic material; - at least one conduit configured for the transport of a process gas and comprising at least one opening (7) for introducing the process gas into said process volume and at least one portion of conduit (8) arranged inside said at least one container (3) in such a way that it can be surrounded by the incoherent plastic material; - a heating device with at least one radio frequency generator (9) and with at least one electrode (10) connected to said at least one radio frequency generator (9), said at least one electrode (10) being arranged inside said at least one container (3) at a distance (D) from said at least one portion of duct (8) and in such a way as to be able to be surrounded by the incoherent plastic material. 2. Apparatus according to claim 1, wherein said at least one electrode (10) is arranged at a higher level than said at least one opening (7). 3. Apparatus according to claim 1 or 2, wherein said at least one electrode (10) is arranged next to said at least one portion of duct (8); said at least one electrode (10) comprising at least one electrode portion arranged next to said at least one portion of duct (8), in particular in such a way that each section of said at least one electrode portion is arranged at the same vertical height with respect to a corresponding section of said at least one portion of duct (8); said at least one portion of duct (8) being arranged, in particular, in a central vertical zone inside said at least one container (3); said at least one opening (7) being arranged, in particular, at a lower end of said at least one portion of duct (8); said at least one opening (7) comprising, in particular, a process gas diffuser connected to said at least one duct. 4. Apparatus according to any of the preceding claims, wherein said at least one container (3) comprises at least one containment wall (W) delimiting said process volume, said at least one electrode (10) being interposed between said at least one portion of conduit (8) and said at least one containment wall (W). 5. Apparatus according to claim 4, wherein said at least one containment wall (W) is made of electrically conductive material, for example metallic material, and/or wherein said at least one portion of duct (8) is made of electrically conductive material, for example metallic material. 6. Apparatus according to claim 4 or 5, wherein said at least one electrode (10) is arranged in said at least one container (3) in such a way that a part of said process volume, which can be filled with the incoherent plastic material, is interposed between said at least one electrode (10) and said at least one portion of conduit (8), and in such a way that another part of said process volume, which can be filled with the incoherent plastic material, is interposed between said at least one electrode (10) and said containment wall (W). 7. Apparatus according to any of the preceding claims, wherein said at least one electrode (10) is oblong in shape and extends along a longitudinal axis and wherein said at least one duct portion (8) extends along a duct axis parallel to said longitudinal axis; said longitudinal axis being, in particular, arranged vertically; said at least one electrode (10) comprising, in particular, at least one section orthogonal to said longitudinal axis with a maximum transverse dimension of between 10 mm and 60 mm; a minimum distance (D) between said at least one electrode (10) and said at least one duct portion (8) being, in particular, between one eighth and one quarter of a maximum diameter of said at least one container (3). 8. Apparatus according to any preceding claim, wherein said heating device comprises two or more electrodes (10) each of which is arranged in said at least one container (3) so that it can be surrounded by the incoherent plastic material in said process volume, said two or more electrodes (10) being arranged circumferentially around said at least one duct portion (8), in particular around a vertical duct axis; said two or more electrodes (10) being configured, in particular, so that an area occupied by said two or more electrodes (10) in a horizontal cross-section of said process volume is included in a range of 1% to 6% of a total area of said horizontal cross-section, where total area means the maximum area that can be occupied by the incoherent plastic material, thus excluding at least one area occupied by said at least one duct portion (8). 9. Apparatus according to any of the preceding claims, wherein said heating device comprises two or more electrodes (10) each of which is arranged in said at least one container (3) in such a way as to be able to be surrounded by the incoherent plastic material in said process volume; said two or more electrodes (10) having, in particular, dimensions different from each other, said dimensions being measured in a direction parallel to a duct axis of said at least one duct portion (8). 10. Apparatus according to any of the preceding claims, comprising at least one temperature sensor associated with said at least one electrode (10), in particular for detecting a surface temperature of the electrode. 11. Apparatus according to any of the preceding claims, comprising a device for moving the material in the container. 12. Apparatus according to any of the preceding claims, wherein said at least one container (3) comprises at least one material inlet (4) arranged at a height that is higher than both said at least one opening (7), said at least one portion of conduit (8), and said at least one electrode (10), and wherein said at least one container (3) comprises at least one material outlet (5) arranged at a height that is lower than both said at least one opening (7), said at least one portion of conduit (8), and said at least one electrode (10), said at least one container (3) being configured to allow a flow of incoherent plastic material from said at least one material inlet (4) to said at least one material outlet (5); said at least one container (3) comprising, in particular, a vertical axis passing through said at least one material outlet (5) and coaxial with a conduit axis of said at least one portion of conduit (8). 13. Apparatus according to any of the preceding claims, comprising control means configured to control said at least one radio frequency generator (9) based on one or more chemical-physical characteristics of the incoherent plastic material and/or the process gas; said one or more chemical-physical characteristics comprising, in particular, a dielectric constant of a mixture of incoherent plastic material and process gas and/or a filling factor, i.e. a ratio between a volume actually occupied by the incoherent plastic material in the container (3) and a total volume available in the container (3) to contain the incoherent plastic material, and/or a temperature of the incoherent plastic material or the process gas and/or a parameter indicative of the moisture content in the incoherent plastic material or the process gas and/or the chemical composition of the incoherent plastic material. 14. A system for dehumidifying loose plastic material, said system comprising at least one radio frequency (RF) dehumidifying stage and at least one process gas (PG) dehumidifying stage connected to each other with in-line feeding of loose plastic material; said at least one radio frequency (RF) dehumidifying stage comprising, in particular, an apparatus according to any of the preceding claims; said at least one process gas (PG) dehumidifying stage being arranged, in particular, so as to process loose plastic material prior to said at least one radio frequency (RF) dehumidifying stage. 15. A method of dehumidification, in particular using a dehumidification apparatus or system according to any of the preceding claims, said method comprising the steps of: - introduce incoherent plastic material to be dehumidified into a process volume defined by a container (3); - introducing process gas into said process volume through at least one opening (7) of at least one conduit for transporting the process gas, said at least one conduit comprising at least one portion of conduit (8) arranged inside said container (3) in which the process gas flows from top to bottom, said at least one portion of conduit (8) being surrounded by the incoherent plastic material; - emitting radio frequency waves by means of at least one electrode (10) surrounded by the incoherent plastic material, said at least one electrode (10) being placed at a distance (D) from said at least one portion of duct (8). 16. A method according to claim 15, comprising, prior to said step of introducing incoherent plastic material, a preliminary step of heating and dehumidifying the incoherent plastic material inside a dehumidification hopper by means of a process gas and a step of transferring the processed material exiting said dehumidification hopper into said process volume; said incoherent plastic material comprising, in particular, recycled polymeric material PCR. 17. A method according to claim 15, comprising a step of transferring the processed material exiting from said process volume to a dehumidification hopper within which the loose plastic material is dehumidified by a process gas. 18. A method according to any of claims 15 to 17, comprising a step of controlling the emission of radio frequency waves, in particular by controlling a radio frequency generator (9), based on one or more chemical-physical characteristics of the incoherent plastic material and/or the process gas; said one or more chemical-physical characteristics comprising, in particular, a dielectric constant of a mixture of incoherent plastic material and process gas and/or a filling factor, i.e. a ratio between a volume actually occupied by the incoherent plastic material in the container (3) and a total volume available in the container (3) to contain the incoherent plastic material, and/or a temperature of the incoherent plastic material or of the process gas and/or a parameter indicative of the moisture content in the incoherent plastic material or in the process gas and/or the chemical composition of the incoherent plastic material.