| WO2013092554A1 | 2013-06-27 | |||
| WO2010109403A1 | 2010-09-30 | |||
| WO2010057695A2 | 2010-05-27 | |||
| WO2010089721A1 | 2010-08-12 |
| US4532319A | 1985-07-30 | |||
| US4792573A | 1988-12-20 | |||
| US6288131B1 | 2001-09-11 | |||
| US6449875B1 | 2002-09-17 | |||
| US4161578A | 1979-07-17 | |||
| US4064112A | 1977-12-20 | |||
| US5714571A | 1998-02-03 | |||
| US4698917A | 1987-10-13 | |||
| EP0312741A2 | 1989-04-26 | |||
| EP2511635A1 | 2012-10-17 | |||
| US7137802B2 | 2006-11-21 | |||
| EP2511635A1 | 2012-10-17 | |||
| US20090249955A1 | 2009-10-08 |
| CLAIMS 1. A treatment method (1) for flowable material (W) comprising - introducing a certain quantity of said material (W) to be subjected to said treatment into a container body (101); - generating a desired degree of vacuum in said container body (101) by way of a vacuum generation device operatively connected to said container body (101); - regulating the temperature of said material (W) by way of a temperature regulation device in such a manner as to adjust said material (W) to a desired treatment temperature (TT) such that said material (W) is subjected to a treatment which generates secondary products from said material (W); - feeding a treatment fluid (G) capable of binding said secondary products into said container body (101) and - extracting from said container body (101) a waste fluid (G') containing said treatment fluid (G) and said secondary products by way of said vacuum generation device; in which said treatment fluid (G) is water and said material being treated is PET. 2. A method according to the preceding claim, wherein said fluid (G) is pretreated in an appropriate pretreatment device (11) before said feeding into said container body (101). 3. A method according to the preceding claim, wherein said pretreating involves varying the temperature of said fluid (G) by way of a further temperature regulation device operatively connected to said pretreatment device (11) for cooling or heating said fluid (G). 4. A method according to claim 2 or 3, wherein said pretreating involves degassing said fluid (G) by generating a desired degree of vacuum in said pretreatment device (11) in order to promote the escape of gases present in said fluid (G). 5. A method according to claim 4, wherein said pretreatment involves, prior to said degassing, aerating said fluid by injecting a desired operating fluid into said fluid (G). 6. A method according to any one of the preceding claims, wherein said temperature regulation involves heating said material being treated (W) in said container body (101), preferably by way of infrared radiation heating means. 7. A method according to any one of the preceding claims, wherein said feeding and said extracting are modulated such that the residence time (τ) of said fluid (G) in said container body is less than 90 s. 8. A method according to any one of the preceding claims, wherein said treatment is PET crystallisation, said secondary products comprising ethylene glycol. 9. A method according to any one of the preceding claims, wherein said temperature regulation involves heating said material (W) in said container body (101), preferably by way of infrared radiation heating means, up to said treatment temperature (TT). 10. A method according to any one of the preceding claims, wherein said material being treated (W) is a plastics material selected from a group comprising PET, PA, PLA, PC or PMMA. 11. A method according to any one of the preceding claims, wherein said treatment is SSP (Solid State Polycondensation), said material (W) is PET and said secondary products comprise acetaldehyde. 12. A treatment apparatus (1) for flowable material (W) comprising - a treatment device (100) capable of receiving a certain quantity of said material (W) to be subjected to said treatment, in particular a treatment in which said material releases secondary products; - a feed device for feeding a fluid (G) capable of binding said secondary products in said treatment device (100); - a temperature regulation device for regulating the temperature of said material (W) in said treatment device (100) in order to adjust said material (W) to a desired treatment temperature such that said material is subjected to a treatment which generates secondary products from said material (W); - a vacuum generation device for generating a desired degree of vacuum in said container body (101) and for extracting from said container body (101) a waste fluid (G') containing said fluid (G) and said secondary products. 13. Apparatus according to the preceding claim, wherein said temperature regulation device is an infrared radiation heating device. 14. Apparatus according to claim 12 or claim 13, and further comprising a pretreatment device (11) for pretreating said fluid (G) before feeding it into said container body (101). 15. Apparatus according to any one of claims 12-14, and further comprising modulating means (42, 43, 163; 52, 53, 163) for modulating the quantity of fluid (G) fed to and/or the quantity of waste fluid (G') extracted from said container body (101) such that said fluid has a residence time in said container body (101) of less than 90 s. 16. Apparatus according to claim 15, wherein said modulating means comprise regulating valves (42; 52) and/or flow regulators (43; 53) provided on a feed line for said fluid (G) to said container body (101). |
MATERIAL
Description
Field of the invention
The present invention relates to a treatment method and a treatment apparatus for flowable material having the features set out in the pre- characterising clause of the main claim .
The method and apparatus of the invention are particularly suitable for use in the processing method for flowable material in which a heat treatment step, in particular heat treatment by infrared radiation, is required.
The method and apparatus of the invention are particularly suitable for use in the processing method for plastics material, in particular for polyethylene terephthalate (PET).
Although the following description makes reference to treating plastics material, the method and apparatus of the invention may also be used in other sectors, for example in the treatment of a flowable foodstuff.
Background of the invention
PET is a semicrystalline polymer and thus its solid structure is made up of (a) an amorphous phase in which the molecular chains are arranged without any specific order and (b) a crystalline phase in which the molecular chains are arranged in accordance with specific geometric figures.
When PET is heated to a temperature of greater than 272°C, it begins to soften, changing from a glassy state to a rubbery state, in which the polymer chain can be stretched and aligned to form fibres, films or bottles. If the molten material is rapidly cooled, the chains remain locked in a certain orientation and an amorphous material having the typical properties of PET bottles is obtained.
On the other hand, if the material, once stretched, is kept at elevated temperatures, it crystallises, the chains gradually become ordered and the material starts to become opaque, stiffer and less flexible.
This form is known as crystalline PET or cPET, has a softening temperature higher than that of amorphous PET and is capable of withstanding higher temperatures. Crystalline PET may be used for trays and containers capable of withstanding temperatures of as high as 150°C.
PET begins to change from the amorphous state to the crystalline state at approximately 80°C and the highest rate of change is reached at around 165°C.
During crystallisation, the PET releases ethylene glycol which makes the PET "sticky", so tending to stop the material from being flowable, and therefore the ethylene glycol must be removed so that crystallisation can proceed properly and the PET becomes flowable again.
During PET crystallisation, heat must be supplied to the material to prevent the PET from cooling, so suspending crystallisation, and/or to increase the temperature to accelerate the crystallisation process.
The PET may be heated by convection, for example using hot air or nitrogen, by conduction, for example by way of electrical heating elements, by irradiation, for example with infrared radiation lamps, by way of microwaves, for example by way of a magnetron, or indeed by friction, for example by way of rotating blades or discs.
Two or more heating systems may optionally be used simultaneously or in succession.
Heating may be provided while simultaneously evacuating the container holding the material being treated in order to make the process more efficient.
Various treatment devices are known for crystallising PET which heat it using the systems which have just been mentioned.
Some known devices are described for example in US 6449875, US
4161578, US 4064112, US 5714571, US4698917, WO2010109403,
WO2010057695, EP0312741, EP2511635 or US7137802.
However, the known devices exhibit some disadvantages due to the low efficiency of removing ethylene glycol and in general the secondary products which form during the PET crystallisation step.
Said defect is particularly obvious in the case of continuous processes and/or of irregular grain sizes of the material, such as ground preforms, bottles, thermoforming sheets, straps or other articles manufactured from PET.
Heating by conduction, irradiation, friction or microwaves brings about PET crystallisation, but has minimal crystallisation efficiency since the ethylene glycol must move away from the mass of material and disperse in the environment. If the environment is evacuated, glycol extraction is improved under the action of the vacuum, but the overall efficiency of the process is nevertheless low.
Not even in convection systems are good removal of the ethylene glycol and, hence, good efficiency of the PET crystallisation process, achieved due to the non-uniform distribution of air or nitrogen in the mass of material to be treated.
Known crystallisation processes thus have poor efficiency, require long overall times and have sub-optimal results in terms of percentage crystallisation.
Furthermore, the known systems are very costly most particularly because of high energy consumption and/or high capital plant costs.
Known systems for carrying out PET crystallisation require at least 1 hour of treatment at 160°C to achieve percentages of crystallisation of 30-40%. Another example of PET crystallisation with the above-stated systems in contrast requires applying elevated temperatures, 200-230°C, to the material using dehumidified nitrogen to improve ethylene glycol removal, but the plant costs and energy consumption are substantial : this is because PET heated to 200-230°C is sensitive both to oxygen and to hydrolysis and thus not only requires a suitable environment, for example dehumidified nitrogen, but must also be cooled to temperatures of below 180°C in order to come back into contact with the outside environment and be further processed.
Some of the above-mentioned problems may furthermore also be encountered when crystallising plastics materials other than PET or also in some heat treatment processes for foodstuffs. If PET is heated to temperatures of greater than 200°C, slightly below the melting point thereof and in the absence of oxygen, it may undergo an increase in molecular weight in a "regrading" reaction.
Regrading is known as "Solid State Polycondensation", hereafter SSP, and involves forming larger molecules by means of repeated condensation reactions with elimination of molecules of water, ethylene glycol (EG) or diethylene glycol (DEG) and acetaldehyde (AA).
Said reaction brings about an increase in the intrinsic viscosity (IV) of the PET and, hence, in the mechanical characteristics thereof.
The SSP process is also applied to nylon (PA) and to polycarbonate (PC), or to biopolymers such as PLA which, when exposed to elevate temperatures in the absence of oxygen, may undergo an increase in molecular weight. Heating may proceed by convection using hot air or nitrogen, by conduction by way of electrical heating elements, by irradiation with infrared radiation lamps, by way of microwaves with a magnetron, or indeed by friction by way of rotating blades or discs. Two or more heating systems may be used in succession or simultaneously.
Heating may be provided while simultaneously evacuating the container holding the PET being treated to make the process more efficient.
Once the PET has been adjusted to a temperature of between 200°C and 235°C in such a manner as to bring about SSP, the PET is kept for a desired time interval, usually of between 10 and 30 hours, at a temperature such as to bring about SSP.
On completion of the SSP process, or when a desired degree of viscosity is achieved, the PET is cooled in the absence of oxygen and moisture to the safety temperature of 180°C, the temperature below which oxidation and/or degradation of the PET do not occur, before being discharged from the device itself, and/or introduced into the environment and, hence, brought into contact with air and moisture.
At temperatures greater than 180°C in the presence of oxygen, PET is subject to rapid oxidation and/or hydrolytic degradation which ruin its mechanical characteristics, i.e. reduce its intrinsic viscosity, and aesthetic properties such as changing its white colour to yellow, brown or grey. As has been stated, during the SSP process PET releases acetaldehyde, a toxic, teratogenic, mutagenic and carcinogenic substance which consequently cannot be released into the environment but must be captured.
Various treatment devices for carrying out SSP are known, for example those described in US4161578, US4064112 and US5714571, in which the PET is heated by convection.
The known devices exhibit some disadvantages.
When nitrogen is used such as the heating fluid, said devices have very high operating costs due both to the nitrogen costs and to the pretreatment required for the nitrogen itself. Furthermore, the nitrogen extracted from the device must be purified of the acetaldehyde and, in general, the secondary products emitted from the PET during SSP. The operations for purifying the nitrogen of acetaldehyde are particularly costly because they make use of platinum or platinum/palladium catalysts which break the acetaldehyde down into non-toxic compounds, such as for example C0 2 , 0 2 and H 2 0.
Furthermore, such devices, such as in general devices in which the plastics material is heated by convection, do not permit a high level of uniformity of heating to be achieved and, hence, it is possible to create zones in the device in which the PET does not reach a sufficiently high temperature for
SSP and zones in which the PET may partially melt.
Furthermore, the efficiency achievable with said devices is low.
Other devices capable of carrying out SSP of PET are furthermore known from WO2010109403, WO2010057695 and WO2010057695.
Such devices, however, have poor efficiency when it comes to cooling the
PET on completion of the SSP step.
Known SSP processes thus have low efficiency and require extended periods of time most particularly due to poor cooling efficiency.
The object of the present invention is to provide methods for heat treating flowable material which make it possible to increase the efficiency of the treatment itself and to improve removal of any secondary products generated during the heat treatment. Another object is to provide a method which makes it possible to increase the efficiency of crystallisation and/or SSP of PET, while at the same time reducing energy consumption and improving the quality of the output material .
A further object of the invention is to optimise removal of the ethylene glycol generated during crystallisation of the PET and/or of the acetaldehyde generated during SSP of the PET.
Another object is to provide a method for dehumidifying a plastics material or foodstuff in which control of the moisture content of the material being treated is optimised and removal of the moisture from the material being heat treated is optimised.
Another object is to reduce the cooling time for PET on completion of an SSP treatment.
A first aspect of the invention provides a treatment method for flowable material comprising feeding a certain quantity of material to be treated into a container body, subjecting the material to a desired degree of vacuum in the container body, regulating the temperature of the material in such a manner as to adjust it to a desired treatment temperature, such that said material is subjected to a treatment which generates secondary products and injecting a treatment fluid into said container body and extracting the fluid together with the secondary products from the container body by way of vacuum generation means.
In a preferred version of the invention, the treatment is crystallisation of PET and the treatment fluid is water.
Another aspect of the invention provides a treatment method for flowable material comprising introducing a certain quantity of material to be treated into a container body, regulating the temperature of the material in such a manner as to adjust it to a desired treatment temperature, such that the material is subjected to a treatment which generates secondary products, feeding a treatment fluid capable of binding said secondary products into said container body and generating a desired degree of vacuum in the container body and extracting from the container body a waste fluid containing the treatment fluid and the secondary products by way of a vacuum generation device of the container body, which method provides modulating feeding of the treatment fluid and extraction of the waste fluid such that the residence time of the treatment fluid in the container body is less than 90 s.
Preferably, the residence time of the fluid is less than 50 s, still more preferably less than 10 s.
In a preferred version of the invention, the treatment is SSP of PET and the treatment fluid is water.
In other versions, the treatment is dehumidification of a flowable plastics material or foodstuff, and the treatment fluid is water.
In other versions, the treatment is cooling a flowable plastics material or foodstuff, and the treatment fluid is water.
The treatment fluid is fed into the container body after a desired time interval with regard to introduction of the material to be treated into the container body, such that the material may firstly be adjusted to the treatment temperature and the treatment itself has started. Said time interval depends on the type of treatment to be carried out; in the case of SSP the treatment fluid is fed in after 15-30 min from the introduction of the material to be subjected to SSP, in the case of dehumidification the treatment fluid is fed in after approximately 20 min.
One version of the invention may provide pretreating the treatment fluid before it is injected into the container body.
Another aspect of the invention provides a treatment apparatus for flowable material comprising a treatment device capable of receiving a certain quantity of material to be subjected to treatment, in particular a treatment in which the material releases secondary products; a feed device for feeding a fluid capable of binding the secondary products in the treatment device; a temperature regulation device for regulating the temperature of the material in the treatment device in order to adjust the material to a desired treatment temperature such that the material is subjected to a treatment which generates secondary products; a vacuum generation device for generating a desired degree of vacuum in the container body and for extracting therefrom a waste fluid containing the treatment fluid and the secondary products, and modulating means for modulating the quantity of treatment fluid fed to and/or the quantity of waste fluid extracted from the container body such that the treatment fluid has a residence time in the container body of less than 90 s.
Despite explicit reference being made below to PET, the invention may be applied to heat treatments, in particular dehumidification, for plastics materials other than PET, for example PA (nylon), PC (polycarbonate) or biopolymers such as PLA (polylactic acid).
The invention may be applied to any type of flowable material which requires a heat treatment, including optional cooling, such as for example foodstuffs.
The invention applies to solid state regrading of plastics material (SSP), preferably of PET.
According to the invention, the treatment methods are carried out and regulated in such a manner as to avoid melting the plastics material being processed.
The features and advantages of the present invention will become clear from the following detailed description of a preferred embodiment thereof, which is given purely by way of non-limiting example with reference to the appended drawings in which :
Figure 1 is a schematic view of a treatment apparatus according to the invention;
Figure la is a magnified view of a fluid feed device of the treatment apparatus of Figure 1 ;
Figure 2 is a variant of the treatment apparatus of Figure 1 ;
Figure 3a is a front view of a diffusion element;
Figure 3b is a magnified side view of a variant of a diffusion element.
Figure 1 is a schematic representation of a treatment apparatus 1 for treating flowable material according to the invention.
The treatment apparatus 1 is particularly suitable for treating plastics material, such as PET, PA, PC, PMMA, biopolymer such as PLA, etc., foodstuffs such as coffee, rice, peanuts, pasta or also chopped herbs, clay, etc. The invention may be applied to SSP and/or crystallisation of plastics materials other than PET, for example PA, PC, PLA, or also to heat treatment, in particular dehumidification, of PET and/or of the above- mentioned plastics materials or foodstuffs.
The treatment apparatus 1 of the invention is suitable for treating flowable material in the form of granules, powder, flakes, as a paste or liquid, also originating from grinding and, hence, of the irregular shape.
The invention may furthermore be applied to any type of flowable material, preferably in the solid state, which requires a heat treatment preferably in the absence of oxygen, including optional cooling, such as for example flowable foodstuffs.
Furthermore, the treatment apparatus 1 is suitable for treating flowable material which is new or originates from existing manufactured articles. The treatment apparatus 1 may be used in a conventional plastics processing plant, or included in plants for treating flowable material in which a heat treatment step is provided.
The treatment apparatus 1 comprises a treatment device 100 capable of containing a desired quantity of flowable material to be treated.
The treatment device 100 is suitable for carrying out a plurality of treatment steps, in particular heat treatment steps which require the application of heat to or removal of heat from the flowable material .
The device 100 comprises an inlet portion for introducing a desired quantity of material to be treated W into the device 100 itself and an outlet portion for discharging the material W at the end of the planned treatment steps. The device 100 may be produced for example according to the teaching of one of the following patent documents: WO2010089721, WO2010109403, WO2010057695, US4698917, US7137802, EP0312741 or EP2511635A1. The method of the invention may, however, also be implemented in other existing treatment devices for plastics materials, making it possible to increase the efficiency thereof.
The device 100 comprises a container body 101, the shape of which is selected on the basis of the characteristics and/or quantity of the material to be treated. In one version, the treatment device 100 is provided with a vacuum generation device, not shown in the Figures, operatively connected to said container body and arranged to generate a desired degree of vacuum within the container body 101, during treatment of the flowable material .
In one version, the treatment device 100 is provided with at least one temperature regulation device, not shown in the figures, for supplying/removing heat to/from the flowable material present in the container body 101, in a preferred version, an infrared radiation heating device.
Such a solution is particularly suitable in the case of a certain degree of vacuum being created in the container body 101, since infrared radiation is more efficient and versatile than other heating methods in an environment under vacuum .
The combination of infrared radiation and vacuum makes it possible to increase the heating rate of the material being treated and to adjust some materials, such as for example PET, to temperatures close to the surface melting point. This makes it possible to make the SSP step 3 to 10 times faster than known systems.
In a version which is not shown in the figures, the treatment device 100 is provided with a mixing element for mixing the material being treated in the container body 101 in order to promote homogeneous heating of the material being treated W.
The treatment apparatus 1 furthermore comprises a feed apparatus 5 for feeding a treatment fluid G from a fluid source 2 to the interior of the container body 101, as indicated by the arrow F. In the version shown in Figure 1, the feed apparatus 5 is provided with a feed device 11, shown in greater detail in Figure la.
In some preferred versions, the treatment fluid G is water, preferably degassed, or nitrogen, preferably dehumidified, as described in greater detail below.
In the case in which the fluid G is water, the fluid source 2 could be the water mains; in the case in which the fluid G is nitrogen, the fluid source 2 is a device for generating nitrogen from air, or a container preloaded with liquid nitrogen. The nitrogen is preferably dehumidified before being introduced into the container body 101.
The feed apparatus 5 comprises first connecting elements 3 and second connecting elements 4 for operatively connecting the feed device 11 respectively to the fluid source 2 and to the container body 101.
The first connecting elements 3 comprise a first connecting line 32 connected at the opposite two ends thereof respectively to the fluid source
2 and to the feed device 11 in such a manner as to permit passage of treatment fluid G from the fluid source 2 to the feed device 11.
The first connecting line 32 is provided with a first regulating valve 31 for opening/closing the first connecting line 32 to permit/prevent passage of the treatment fluid G from the fluid source 2 to the feed device 11.
A first flow regulator 33 is provided on the first connecting line 32 for varying the cross-section thereof and, hence, the flow rate of fluid G entering the feed device 11 when the first regulating valve 31 is open. In one version, the first regulating valve 31 incorporates the first flow regulator 33.
In one version which is not shown, a pump may be provided on the first connecting line 32 for feeding the fluid G from the fluid source 2 to the feed device 11.
The second connecting elements 4 comprise a second connecting line 42 connected at the opposite two ends 42a and 42b thereof respectively to the feed device 11 and to the container 101 to permit flow of the treatment fluid G from the feed device 11 to the treatment device 100.
The second connecting line 42 is provided with a second regulating valve
41 for opening/closing the second connecting line 42 to permit/prevent flow of fluid G from the feed device 11 to the treatment device 100.
The second end 42a of the second connecting line 42 is provided with a diffuser element 44 which opens into the container body 101 for facilitating entry of the fluid G into the container body 101 and improving the diffusion thereof in the material being treated W.
The second connecting line 42 may be provided with a second flow regulator 43 for varying the cross-section thereof, in such a manner as to vary the flow rate of fluid G entering the treatment device 100. In this case too, in one version, the second regulating valve 41 incorporates the second flow regulator 43.
In a version which is not shown, a flowmeter is provided on the second connecting line 42 for measuring the quantity of fluid G entering the device 100.
The feed apparatus 5, in particular the first and second connecting elements 3 and 4, are airtight relative to the outside environment, such that air does not seep in on passage of the fluid G from the fluid source 2 to the treatment device 100.
The feed device 11 comprises a body 11a arranged for containing a certain quantity of treatment fluid G and is suitable for pretreating the treatment fluid G before feeding it to the container body 101.
The body 11a is of variable capacity depending on the quantity of flowable material being treated and on the type of treatment to be carried out in the treatment device 100 and may be cylindrical in shape or also have a polygonal base and is made from a material capable of containing gases and/or liquids.
In one embodiment the body 11a is airtight and leakproof and is made from material capable of withstanding even high levels of vacuum, possibly being made from metal, for example steel, or also from glass or plastics, of a thickness appropriate to the operating conditions.
The feed device 11 may be provided with minimum level sensor 7 and a maximum level sensor 8 which respectively indicate the minimum and maximum levels of the fluid G in the body 11a.
Other versions may have additional sensors provided for measuring the quantity of treatment fluid G in the body 11a, for example intermediate level sensors between the minimum and maximum, or load cells, or a laser level sensor which continuously senses any variation in the filling level of the feed device 11.
The feed device 11 moreover comprises a further temperature regulation device 135, more readily visible in Figure la, for pretreating the treatment fluid G present in the body 11a by heating or cooling it. In the version shown, the temperature regulation device 135 comprises a shell 12 positioned externally to the body 11a and shaped such that, between the outer wall of the body 11a and the shell 12, an interspace 13 is defined in which a temperature regulation fluid, for example water or oil, at a desired controlled temperature is circulated.
The shell 12 is provided with at least one inlet valve 130 and an outlet valve 131 for the temperature regulation fluid in the interspace 13 : the inlet 130 and outlet 131 valves are arranged such that passage of the temperature regulation fluid in the interspace 13 is uniform and that the treatment fluid G is heated, or cooled, uniformly.
The interspace 13 may be provided with bulkheads arranged to create a desired arrangement of the circuit for the temperature regulation liquid which is capable of increasing the uniformity of heating or cooling.
Temperature probes, which are not shown, may be provided for controlling the temperature of the temperature regulation fluid entering and exiting the interspace 13.
Depending on whether the temperature of the temperature regulation fluid in the interspace 13 is higher/lower than the temperature of the treatment fluid G in the feed device 11, the fluid G in the feed device 11 may be heated or cooled.
A version which is not shown may be provided with a plurality of inlet and/or outlet valves, the interspace 13 being subdivided into two or more mutually independent portions, in such a manner as to define multiple independent temperature regulation circuits.
In one version which is not shown, the feed device 11 is furthermore provided with a control device capable of controlling the flow rate and/or temperature of the temperature regulation fluid in the interspace 13.
Depending on whether the temperature of the temperature regulation fluid is higher/lower than the temperature of the treatment fluid G, the latter is heated or cooled in the feed device 11.
In one version which is not shown, the feed device 11 is furthermore provided with a control device capable of controlling the flow rate and/or temperature of the temperature regulation fluid in the interspace 13. The feed device 11 is furthermore provided with temperature probe 9 for measuring the temperature of the treatment fluid G within the body 11a. The temperature probe 9 sends a signal relating to the measurement made to the control device of the temperature regulation circuit in order, if necessary, to vary the flow rate and/or temperature of the temperature regulation fluid.
In this manner, the temperature of the treatment fluid G in the body 11a is effectively controlled.
The feed device 11 is furthermore provided with a connecting assembly 6 for connecting the feed device 11 to an operating fluid source for introducing a desired operating fluid into the interior of the body 11a.
In such a case, pretreatment may involve introducing an operating fluid, preferably water, or air, pressurised, or at ambient pressure, into the treatment fluid G, as described in greater detail below.
The connecting assembly 6 comprises a line 62 engaged at a first end 62a thereof on the body 11a of the feed device 11 and provided at a second end 62b thereof opposite to the first end 62a with a valve 61 for opening/closing the connection of the feed device 11 with the operating fluid source.
In a version which is not shown, the valve 61 may be mounted directly on the body 11a of the feed device 11.
The line 62 is provided with a flow regulator element 63 for varying the cross-section of the line 62 and, hence, the flow rate of operating fluid entering the feed device 11. In a version which is not shown, the valve 61 incorporates the flow regulator element 63.
The feed device 11 is furthermore provided with a vacuum generation device 16 comprising a vacuum pump 163 operatively connected by way of a connecting tube 162 to the feed device 11 in order to generate a desired degree of vacuum within the body 11a in such a manner as to pretreat the treatment fluid G by subjecting it to a desired degree of vacuum .
The connecting tube 162 is provided with a second valve 161 for opening/closing the connection between the feed device 11 and the vacuum pump 163 : when the second valve 161 is open and the vacuum pump 163 is on, the body 11a may be placed under a vacuum .
In one version, the vacuum pump 163 is actuated in such a manner as to generate in the body 11a a certain negative pressure which is preferably greater than or equal to that present within the treatment device 100.
By subjecting the fluid G to a certain degree of vacuum in the body 11a, it is possible to improve the characteristics of the fluid G for treatment in the container body 101, before introducing it into the container body 101 itself, as explained in greater detail below.
In one version which is not shown, the feed device 11 is directly connected to the treatment device 100 by way of an appropriate connecting tube optionally provided with a valve, in such a manner that the treatment device 100 and the feed device 11 are at the same negative pressure.
The feed device 11 comprises at least one agitation device for agitating the treatment fluid G present in the body 11a and to promote the escape of any gas present in the fluid G, as described in greater detail below.
In the version shown in Figure la, the feed device 11 comprises a mechanical vibrator 150 operatively connected to the feed device 11, such that when the mechanical vibrator 150 is actuated the vibrations from the vibrator are transmitted by contact with the walls of the body 11a and thence to the treatment fluid G.
The feed device 11 furthermore comprises a spindle 151 connected to a motor which is not shown in the figure and provided with a rotary shaft and a plurality of mixing elements extending radially from the shaft. The spindle 151 is capable of being set in rapid rotation, clockwise, anticlockwise or a combination, in such a manner as to create rapid movement of the treatment fluid G in the feed device 11.
Versions of the feed device 11 which are not shown may be provided with a single agitation device for agitating the treatment fluid G in the body 11a. Other versions which are not shown may be provided with other agitation devices as an alternative or addition to the mechanical vibrator 150 and the spindle 151, to shake the feed device 11 and hence the treatment fluid G abruptly in such a manner as to facilitate extraction of any air. Figure 2 shows an alternative version of the feed apparatus 5' which comprises a connecting line 52 connected at the opposite two ends 52a and 52b thereof respectively to the fluid source 2 and to the treatment device 100 to permit passage of fluid G from the fluid source 2 to the interior of container body 101, as indicated by the arrow F. In said version, the fluid G flows directly from the fluid source 2 to the container body 101.
The connecting line 52 is provided with a regulating valve 51 for opening/closing the link between the fluid source 2 and the treatment device 100 : when the regulating valve 51 is open, the fluid G flows from the fluid source 2 to the treatment device 100 by way of the connecting line 52, whereas when the regulating valve 51 is closed passage of fluid G from the fluid source 2 to the treatment device 100 is interrupted.
The feed apparatus 5' comprises a flow regulator 53 for varying the cross- section of the connecting line 52, for varying the flow rate of fluid G in the connecting line 52 and, hence, the quantity of treatment fluid G entering the treatment device 100.
In a variant which is not shown, the regulating valve 51 incorporates the flow regulator 53.
The feed apparatus 5' may furthermore comprise a flowmeter 54 for measuring the quantity of fluid G entering the treatment device 100.
The end 52b of the connecting line 52 engaged in the treatment device 100, is provided with a diffuser element 44 for improving entry and diffusion of the fluid G into the interior of the container body 101 and, hence, into the material being treated W.
Said version of the feed apparatus 5' is preferably used in the case in which the treatment fluid G is a gas, in particular nitrogen, and/or in those cases in which it is not necessary to subject the fluid G to pretreatments in the body 11a between the fluid source 2 and the treatment device 100, or when the treatment fluid G arrives from the fluid source 2 under optimum conditions for introduction into the container body 101, as explained in greater detail below. In a version which is not shown, the feed apparatus 5' is provided with a pump for conveying the fluid G to the interior of the feed apparatus 5' from the fluid source 2 to the treatment device 100.
Figures 3a and 3b show two possible variants of the diffuser element 44: in the version of Figure 3a, the diffuser element 44 is provided with a plurality of holes 441 having a smaller diameter than the cross-section respectively of the connecting line 52 or of the second connecting line 42, capable of subdividing the fluid G entering the container body 101 into a plurality of ducts, so as to improve the diffusion thereof in the material being treated; in the version of Figure 3b, the diffuser element 44 is provided with a single outlet hole 441' having a smaller cross-section than the cross-section respectively of the connecting line 52 or of the second connecting line 42 and which may be circular, elliptical or rectangular in shape.
Versions which are not shown may be provided with other configurations of the diffuser element 44 suitable for optimising entry and diffusion of the fluid G in the container body 101.
Other versions which are not shown may be provided with multiple inlets for the fluid G and hence multiple diffusers 44 on the container body 101 for further improving diffusion of the fluid G in the container body 101. During operation, a desired flowable material W, for example a plastics material such as PET or PA to be subjected to a desired heat treatment, is introduced into the container body 101 of the treatment device 100, as indicated by the feed arrow Fl .
The treatment to be carried out in the treatment device 100 is preferably a treatment which involves the emission of secondary substances from the flowable material being treated and/or which requires an oxygen-free environment and/or which requires specific temperature and pressure conditions, preferably PET crystallisation, SSP or dehumidification of plastics materials or foodstuffs.
The material to be treated W is adjusted, by way of the temperature regulation device, to a treatment temperature T T at which the treatment proceeds. Preferably, the treatment to be carried out requires specific temperature and pressure conditions and thus provision is made to vary the temperature and pressure of the flowable material W in the container body 101.
In a preferred version, the treatment to be carried out is crystallisation of plastics material, preferably PET, which proceeds at a temperature of between 80° and 180°C with production of ethylene glycol .
In other cases, the treatment to be carried out is dehumidification of a plastics material or foodstuff, for which purpose it is necessary to heat the material to be dehumidified, as a consequence of which water vapour is generated from the material being treated.
In preferred version, a desired degree of vacuum is generated in the container body 101 by way of the vacuum generation device, in the case of PET the container body 101 may be adjusted to a negative pressure of between -400 and -999 mbar, absolute vacuum . In the case in which the feed device 11 is connected directly to the treatment device 100, the vacuum pump 163 may be used.
In one version, the flowable material W is heated up to the treatment temperature T T , at which the treatment proceeds, before being introduced into the container body 101, and/or after having been introduced into the container body 101, in this latter case by way of the temperature regulation device of the container body 101.
The material to be treated W is kept at the treatment temperature T T for a period of time which is sufficient to bring about the desired treatment or a certain degree of crystallisation, or regrading, or a certain moisture content.
In the case of PET crystallisation, the PET is heated to a temperature of 80- 100°C, or to a temperature at which glass transition begins resulting in partial crystallisation of the PET.
When the material being treated begins to release secondary products, the treatment fluid G capable of binding the secondary products released by the material being treated W is fed in using one of the methods discussed above and, by way of the vacuum generation device, a waste fluid G' containing the treatment fluid G together with secondary products released by the material being treated W is extracted as indicated by the arrow F2 in Figures 1 and 2.
In this manner, treatment of the flowable material is promoted, with yields being increased and treatment times reduced.
In the case of PET, when PET begins to crystallise and release ethylene glycol, the treatment fluid G is fed in and a waste fluid G' containing the treatment fluid G and the ethylene glycol is extracted, promoting removal of the ethylene glycol from the container body 101 and, hence, crystallisation of the PET, as described in greater detail below.
In the case in which the material being treated is virgin amorphous PET and the fluid G is water, the waste fluid G' is water vapour and ethylene glycol .
In the case in which the material is recycled PET, other secondary products are also released during crystallisation, for example residues of caustic soda used during washing, or residual chemical contaminants on the surface of the material, such as for example toluene, chlorobenzene, chloroform, methyl salicylate, phenyl cyclohexane, benzene, benzophenone, methyl stearate, etc.
In the case in which the treatment is dehumidification, the fluid G used is air or nitrogen and a waste fluid G' containing air or nitrogen and water released by the material being treated is extracted from the container body.
In a preferred version, the treatment to be carried out is SSP of a plastics material, preferably PET, which proceeds at a treatment temperature T T of between 200°C and 235°C with production of acetaldehyde and possibly other secondary products.
The PET to be subjected to SSP is fed into the container body 101 and initially subjected to dehumidification if necessary, for example as described in WO2010109403 and/or WO2010057695, and once it has reached the desired moisture content, is heated in the absence of oxygen to the treatment temperature T T . The material to be treated W is kept at the treatment temperature T T for a period of time which is sufficient to bring about the desired treatment or a certain degree of crystallisation, or regrading, or a certain moisture content.
In the case of SSP, the PET is kept under the suitable negative pressure and temperature conditions for a period of time usually of between 2 and 30 hours, which is selected on the basis of the final intrinsic viscosity (IV) which it is desired to achieve, or on the basis of the degree of regrading to be obtained.
Once certain time interval since the material W was introduced into the container body 101 has elapsed, the method of the invention provides feeding the treatment fluid G into the container body 101 for cooling the PET and for binding the secondary products released by the PET.
The treatment fluid, preferably water, is fed into the container body once a desired time interval since the material to be treated W was introduced into the container body 101 has elapsed such that the material W may firstly be adjusted to the treatment temperature T T , when it has been introduced at a temperature other than the treatment temperature T T , and the treatment itself with release of the secondary products has begun. Said time interval depends on the type of treatment to be carried out, in the case of SSP it is approximately 15-30 min, in the case of dehumidification approximately 20 min.
The water is introduced at a temperature of 80-95°C and removed by way of the vacuum generation device, such that the residence time of the water in the container 101 is less than 50 s, still more preferably less than 10 s, together with the secondary products generated by the PET.
In this manner, treatment of the flowable material is promoted, with yields being increased and the necessary treatment times reduced.
On completion of the SSP, or when the PET has reached a desired degree of regrading, water may be fed into the container 101 to cool the PET down to the safety temperature in the absence of oxygen.
In this case, the water is fed in at a temperature of 5-10°C, or less than the safety temperature of the PET, and extracted from the container body by way of the vacuum generation device, together with secondary products released by the PET, in such a manner as to avoid hydrolysis or degradation of the PET.
In this case too, the quantity of water fed in and extracted is modulated such that the residence time of the water in the container body is less than 50 s, preferably less than 10 s, in order to avoid PET degradation.
The rate of cooling of the PET and the rate and efficiency of acetaldehyde removal from the PET are increased.
In the case of SSP, the treatment fluid G is fed in in such a manner as to ensure the PET remains in the absence of oxygen in order to avoid PET degradation .
The treatment fluid G is fed in until the PET is cooled to a safety temperature of 180°C at which it can be discharged from the container body 101 and introduced into the environment.
When the apparatus of Figure 2 is used, the fluid G is fed in by opening the regulating valve 51, so connecting the source 2 of fluid G to the container body 101.
The flow rate of treatment fluid G is modulated by acting on the regulating valve 51 and/or on the flow regulator 53 or optionally on a flowmeter which is not shown in figures.
Flow rate of the treatment fluid G from the fluid source 2 to the treatment device 100 proceeds by pressure difference since the container body 101 is under a vacuum or, in a version which is not shown, by way of a pump suitable for conveying the fluid G from the fluid source 2 to the treatment device 100.
The pump is used when the pressure difference between the treatment device 100 and the fluid source 2 is sufficient to permit appropriate feed of the treatment fluid G into the container body 101, or in order to increase the feed rate thereof.
The treatment fluid G in the container body 101 comes into contact with a hot environment, increases in volume and tends to diffuse uniformly in the container body 101 and, hence, in the flowable material W being treated, according to Fick's law. Once the required quantity of treatment fluid G has been injected into the container body 101, the regulating valve 51 is closed. In the case of PET, the fluid G may be water, in which case a quantity of water equal to 1- 1.5% by weight of the material being treated W is fed in. Said quantity has been found to be suitable for carrying out crystallisation. Optionally, were it to prove necessary, the operation of feeding treatment fluid G to the container body 101 may be repeated using the methods stated above. In the case in which the treatment device 100 is under a vacuum, it is preferable to feed the treatment fluid G such that injection takes approximately 5-10 min or more, so as not to overload the vacuum generation device and to maintain a desired degree of vacuum in the container body 101.
Feeding in all the required treatment fluid G in few seconds would excessively overload the vacuum generation device, so it is preferable to spread feed of the treatment fluid G over time, ensuring that it takes 5-10 minutes.
The duration of feed is modulated by varying the cross-section of the feed line in the case of continuous feed, or by opening/closing the feed line valve several times in the case of discontinuous feed.
During the PET cooling step after SSP treatment, the treatment fluid G cools the flowable material W and dramatically reduces the time required to reach the safety temperature. In the case of PET, the treatment fluid G is fed at a temperature of between 5°C and 10°C, in the case in which the treatment fluid G is nitrogen it is even fed at a temperature of less than 0°C.
The method provides feeding a desired quantity of treatment fluid G into the container body 101 and subsequently closing the regulating valve 51. If the treatment fluid G is water, a quantity of water equal to 1-1.5% by weight of the material being treated W is fed at a temperature of between 5°C and 10°C which is sufficient to reduce the temperature of the PET by 3-5°C within a few seconds. In order to reduce the temperature of the material being treated W by 20- 50°C, the operation of feeding water into the water container body 101 is repeated several times, as explained in greater detail below.
Since PET at a temperature of greater than 180°C is susceptible to hydrolysis, with associated degradation and hence loss of viscosity, the waste fluid G' must be removed from the container body 101 within short periods of time, such that the residence time τ of the fluid in the container body 101 is of the order of some tens of seconds, preferably less than 50 s, still more preferably less than 10 seconds.
The method of the invention thus provides extracting a waste fluid G' containing the treatment fluid G and the secondary products released by the material being treated W from the container body 101 by way of the vacuum generation device, as indicated by arrow F2.
If the material being treated is amorphous virgin PET and the treatment fluid G is water, the waste fluid G' is water vapour with ethylene glycol and acetaldehyde.
If the material is recycled PET, other secondary products are also released during SSP, for example residues of caustic soda used during washing, or residual chemical contaminants on the surface of the material, such as for example toluene, chlorobenzene, chloroform, methyl salicylate, phenyl cyclohexane, benzene, benzophenone, methyl stearate, etc.
Said secondary products are efficiently removed with the waste fluid.
In this manner, it is possible to treat recycled PET such that it can again come into contact with foodstuffs ("super-clean" process), the characteristics of the PET are further improved, especially from the standpoint of a reduction in acetaldehyde.
The vacuum generation device of the treatment device 100 is activated again once the fluid G has been fed in, in such a manner as to generate and/or maintain a desired degree of vacuum in the container body 101 or it may also be kept active during the feed step of fluid G to the treatment device 100.
One version provides operating the vacuum generation device simultaneously during feed of the treatment fluid G, in order to extract the treatment fluid G, together with the secondary products, from the container body 101 within extremely short periods of time and to maintain the desired degree of vacuum in said container body.
Feed of the treatment fluid G and/or extraction of the waste fluid G' is furthermore modulated such that the residence time τ has the above-stated values.
To this end, the quantity of treatment fluid G introduced into the container body 101 may furthermore be modulated : in the case of continuous feed by varying the cross-section of the feed line; in the case of discontinuous feed by performing a number of discrete feed operations by opening/closing the valve of the feed line several times and, in each feed operation, feeding quantities of treatment fluid G corresponding to 1-1.5% by weight of the PET being treated in the container body 101.
If discontinuous operation is used, a quantity of water corresponding to approximately 1-3%, preferably 1-1.5%, by weight of the quantity of PET being treated is usually fed in a single feed operation, this making it possible to reduce the temperature of the PET by 5-10°C and the feed operation is repeated a sufficient number of times to adjust the PET to the safety temperature.
If all the fluid necessary for achieving the desired cooling of the PET were introduced into the container body 101 in a single operation, it would not be possible to ensure the above-mentioned residence time τ values and there would a risk of at least partial hydrolysis of the PET.
The overall quantity of fluid to be injected is selected on the basis of the temperature of the material, the form of the material (if in flake form it cools faster than in granule form), the temperature of the fluid, level of vacuum, etc.
It is optionally possible to increase the overall quantity of fluid G fed, increasing it to 5-10% by weight, in order additionally to promote surface cleanliness of the material being treated W.
The water is introduced into the container body 101 when the PET is at a temperature of greater than 200°C and is undergoing SSP. As the water enters a hot environment under a vacuum, it evaporates and diffuses into the PET being processed, cools it and binds the ethylene glycol and acetaldehyde. The water is extracted together with the ethylene glycol and acetaldehyde and any further secondary products from the container body 101 under the action of the vacuum generation device ("stripping").
In this manner, the ethylene glycol and acetaldehyde are very quickly carried away from the container body 101. Cooling of the PET is faster and more efficient than in known systems and the quality of the PET obtained is better.
This is because the PET remains in contact with the exiting ethylene glycol for a shorter period of time: the faster the ethylene glycol is extracted during SSP, the better is the quality of the regraded PET.
Removing the acetaldehyde by way of the water is also important because this improves the compatibility of the PET with foodstuffs.
Furthermore, the cooling water is extracted from the container body in short periods of time, so preventing the PET from hydrolysing.
As stated above, in the case in which the treatment fluid G is water or a fluid containing water, once it has been introduced the treatment fluid G must be extracted by the vacuum generation device in less than 10 seconds, so avoiding hydrolysis in the PET with associated degradation and hence loss of viscosity.
Thus, feed of treatment fluid G is modulated using the methods stated above in such a manner as to ensure residence times of the treatment fluid G in the container body 101 of less than 10 seconds.
If the contact time of the water with the PET is increased at temperatures of greater than 200°C, PET degradation, or a drop in intrinsic viscosity, occurs.
The vacuum generation device is actuated in such a manner as to maintain a negative pressure capable of extracting the treatment fluid G in a few seconds.
In the case in which the treatment is dehumidification, the treatment fluid G used is air or nitrogen and a waste fluid G' containing air or nitrogen and water released by the material being treated W is extracted from the container body. In this case too, the overall efficiency of the process is increased by removing the waste fluid in short periods of time in order to prevent the water from rebinding with the material to be dehumidified.
Furthermore, the temperature regulation device is activated to maintain, or readjust, the material being treated W at/to the treatment temperature T T ; in the case of PET crystallisation, a temperature of approximately 165°C. Furthermore, the temperature regulation device is activated to regulate the temperature of the material being treated W; in the case of cooling after SSP, the temperature regulation device is fed with cooling fluid to increase the rate of cooling of the PET and, hence, to reduce the time required to reach the safety temperature of below 180°C.
The flowable material W is kept within the container body 101 until the desired degree of crystallisation, usually greater than 50%, is obtained, but depending on requirements it is possible to produce a PET with a higher percentage crystallisation level of as much as 75%.
The flowable material W is kept within the container body 101 until the safety temperature suitable for introducing the flowable material into the outside environment is reached; in the case of PET the safety temperature is 180°C.
The flowable material may optionally be kept in the container body 101 for a certain time interval after it has reached the safety temperature before being discharged outside.
Usually in the case of PET, once the treatment fluid G has been injected, the temperature regulation device is actuated to maintain or readjust the PET at/to a temperature suitable for carrying out crystallisation and the fluid G and secondary products are usually extracted for a period of time of approximately 10-15 minutes, after which the crystallised PET is discharged from the container body 101.
Furthermore, the treatment fluid G also makes it possible to regulate the temperature of the material being treated W after the treatment. By feeding the fluid G into the container body 101, optionally at a temperature other than the treatment temperature T T , the material is rapidly adjusted to a desired temperature before it is discharged from the container body 101.
Said arrangement is beneficial for example in the case of PET which, once it has been crystallised, is packaged for sale and must be packaged at a temperature below the crystallisation temperature, or also in the case of coffee which must be cooled before being packaged.
On completion of the treatment, the flowable material W may optionally be kept for a certain time interval in the container body 101 before being discharged outside.
In the case of PET crystallisation, the PET is fed to the container body 101 at 80-100°C or the PET is heated in the container body 101 to 80-100°C, the temperature at which glass transition begins; the vacuum is generated in the container body 101, the treatment fluid G is injected for 5-10 minutes while continuing to generate a vacuum and heat the PET to adjust it to 165°C; on completion of feed of the fluid G, evacuation is continued, as is heating, for a further 10-15 minutes to maintain the conditions for bringing about crystallisation and extracting the glycol . Thereafter, the PET is discharged, optionally after having been cooled.
The apparatus of Figure 1 functions entirely similarly to the above description made with reference to the apparatus of Figure 2, except for the provision of a feed device 11 into which the treatment fluid G is fed because it is subjected to some pretreatments, as described in greater detail below, before it is fed into the treatment device 100.
The pretreatments make the treatment fluid G better suited to stripping the secondary products from the material being treated W and, hence, further increase the efficiency of removal of the secondary products and, hence, the efficiency of the treatment.
The flow rate of treatment fluid G entering in the body 11a is varied by way of the flow regulator 33, so as to make operation faster or slower as required.
Flow rate of the treatment fluid G from the fluid source 2 to the feed device 11 may proceed by pressure difference, or simply by gravity or also, in a version which is not shown, by way of a pump. The quantity of fluid G fed into the body 11a is controlled by way of the minimum and maximum level sensors 7, 8 or load cells, laser sensors or timers.
The quantity of fluid G is determined depending on the result it is desired to achieve in the treatment device 100, on the material being treated W, and on the type of treatment fluid G used.
Once the desired quantity of fluid G has been introduced into the body 11a, the first regulating valve 31 is closed and the fluid G is subjected to optional pretreatments and subsequently fed to container body 101 by way of the second connecting elements 4, using the methods stated above. The flow rate of treatment fluid G entering in the container body 101 is optionally varied by way of the second flow regulator 43, so as to make operation faster or slower as required.
In this case too, passage of the treatment fluid G from the feed device 11 to the container body 101 may proceed by pressure difference, or simply by gravity, or by way of an optional pump which is not shown .
Once the desired quantity of treatment fluid G has been injected into the container body 101, the second regulating valve 41 is closed. Optionally, the operation of feeding treatment fluid G to the container body may, if necessary, be repeated, as explained above.
As stated, the pretreatments make the treatment fluid G better suited to stripping the secondary products from the material being treated W.
One version provides regulating the temperature of the fluid G in the feed device 11 by heating it or cooling it. To this end, a temperature regulation fluid, for example water, oil, air, etc., at a desired controlled temperature is caused to flow in the interspace 13 to adjust the treatment fluid G to a desired temperature.
Once the desired temperature has been reached, the fluid G is fed into the treatment device 100.
In other versions, the fluid G may be pretreated by being degassed to eliminate any residual air present in the fluid G, for example if the fluid G is water.
Said pretreatment is particularly appropriate in the case in which it is necessary to reduce, or avoid, entry of air into the treatment device 100 in order to improve the treatment process and avoid possible harm to the material being treated W.
To this end, the feed device 11 is evacuated by way of the vacuum generation assembly 16. When the fluid G is placed under a vacuum, the solubility of gases in the fluid G drops, as described by Henry's law, and thus any air or, in general, gases present in the fluid G, escape from the treatment fluid G and may be discharged by way of the vacuum pump 163. The level of vacuum generated in the feed device 11 is preferably in a range of between at least 1/5 of atmospheric pressure and, on the other hand, equal to or slightly less than the negative pressure generated in the treatment device 100.
In this manner, once the treatment fluid G has been pretreated, it can be fed to the treatment device 100 by pressure difference or by gravity, as described above.
One version may provide both heating the treatment fluid G and placing it under a vacuum in the feed device 11 in order further to increase escape of air or gases from the treatment fluid G by reducing the solubility of the gases in the fluid G under the action of temperature and pressure.
Optionally, once the air has been extracted from the fluid G, the treatment fluid G may be cooled before feeding it to the treatment device 100, depending on the temperature of the material being treated and/or the temperature of the fluid G.
In one version, pretreatment involves agitating the fluid G to promote the escape of any gas present in the fluid G, for example by way of the mechanical vibrator 150 or spindle 151.
In the case in which the fluid G is a liquid, for example water, pressurised gas may be introduced into the treatment fluid G present in the feed device 11 (super-saturation) in order further to improve extraction of air or gas from the treatment fluid G.
The pressurised gas may be for example compressed air.
To this end, the feed device 11 is connected by way of the connecting assembly 6 to a source of pressurised gas which is not shown in the figure, for example a compressed air generator. The valve 61 is opened so allowing pressurised gas to enter the feed device 11 and mix with the treatment fluid G. The flow rate of the gas entering the feed device 11 by way of the connecting tube 62 may be varied by acting on the flow regulator 63.
Once the desired quantity of gas has been injected into the feed device 11, the valve 61 is closed again and the feed device 11 is placed under negative pressure by way of the vacuum pump 163, and the treatment fluid G is optionally heated as described above.
Injecting pressurised gas into the fluid G promotes subsequent degassing of the treatment fluid G, as described in US 2009/0249955, under the action of pressure and/or temperature in such a manner as further to reduce the content of gas in the fluid G before introducing it into the treatment device 100.
One version may make provision for the pressurised gas be injected into the feed device 11 when the feed device 11 has already been evacuated and then the feed device 11 may be evacuated once again.
The decision as to which pretreatment(s) to carry out on the fluid G in the feed device 11 is taken depending on the material being treated W and/or the fluid G used and/or the type of treatment to be carried out in the treatment device.
In the case of PET crystallisation, the fluid G which is injected into the container body 101 is preferably water or in any event a fluid suitable for chemically binding ethylene glycol.
The water is preferably injected at a temperature of between 10 and 40°C and may be subjected to degassing in the feed device 11 in order to reduce the gas content thereof so as to protect the PET from any possible oxidation.
The water is introduced into the container body 101 when the PET is at a temperature of 80-100°C and begins to crystallise and release ethylene glycol. As the water enters a hot environment under a vacuum, it evaporates and diffuses into the PET being processed, binding to the ethylene glycol, and is extracted together with the glycol from the container body 101 under the action of the vacuum generation device ("stripping").
The ethylene glycol and also any other secondary products such as caustic soda or diluents in the case that the PET originates from recycling are extracted together with the water.
In this manner, the glycol is very quickly carried away from the container body 101. Crystallisation of the PET is faster and more efficient than in known systems and the quality of the crystallised PET is better. The PET remains in contact with the ethylene glycol exiting with the treatment fluid for a shorter period of time: the faster the ethylene glycol is extracted during crystallisation, the better is the quality of the crystallised PET.
Water is generally injected for crystallisation at room temperature (10- 40°C), also heated up to 90-95°C, in a percentage of 1-3% relative to the quantity of PET being processed, over a period of time of 5-10 minutes. Other fluids which are chemically compatible with ethylene glycol may be used as an alternative to water.
Using water as treatment fluid makes it possible to reduce PET crystallisation costs, not only because crystallisation times are shorter and crystallisation efficiency is high but also because water is an inexpensive fluid which is readily obtainable.
Performing crystallisation under a vacuum makes it possible further to reduce the time required for crystallisation down to 10-20 minutes.
Furthermore, high quality crystallised PET is obtained, namely a uniform material with percentages of crystallisation of above 70%.
Furthermore, in the case that the material has to be packaged in sacks or containers for sale, once the PET has crystallised, it can be kept in the treatment device 100 by injecting fluid G at such a temperature as to cool the PET before it is discharged from the treatment device 100.
In this manner, the temperature of the flowable material W is reduced in extremely short periods of time.
The PET for packaging is usually adjusted at least to a temperature of below 80°C. Furthermore, if the fluid G is water, the material may be moisture- conditioned, so as to adjust it to a stable initial moisture condition.
In the case of SSP of PET, the treatment fluid G is water, preferably fed at a temperature of between 5 and 10°C, which may be subjected to degassing in the feed device 11 in order to reduce the air content thereof so as to protect the PET from any possible oxidation.
Carrying out SSP as described appreciably reduces treatment times and, most particularly, the time for cooling the PET to the safety temperature. For example, in comparison with a vacuum system which heats and cools the material by conduction, as proceeds in tumble dryers, the time for cooling the PET from 220°C to 180°C is cut from 4-5 hours to 30-60 minutes.
Furthermore, in the case that material has to be packaged in sacks or containers for sale, once the PET has reached the safety temperature, it can be kept in the container body 101 by injecting treatment fluid G to adjust the PET to a temperature of less than 80°C before it is discharged from the treatment device 100.
In this manner, the temperature of the flowable material W is reduced in extremely short periods of time.
Furthermore, if the treatment fluid G is water, the PET is moisture- conditioned, so adjusting it to a stable initial moisture condition.
In the case in which the material being treated W is PET at a temperature less than 180°C or coffee and the treatment fluid G is water, is possible to moisture-condition the material prior to packaging by way of the treatment fluid G, so adjusting it to the desired moisture level .
Using water as treatment fluid permits efficient removal of secondary products which are released during the treatment, in particular glycol or acetaldehyde.
Said feature is particularly important where recycled plastics material is used and/or if the intention is to produce plastics material for food-contact purposes which must be of particularly high quality.
The water pretreatments make it possible further to increase the quality of the material obtained and to accelerate the treatments carried out. Furthermore, combined use according to the invention of infrared radiation, vacuum and water permits a particular increase in the efficiency of the methods for treating flowable material according to the invention, making it possible to achieve very high treatment efficiency and extremely short treatment times and a material of high chemical quality.
Furthermore, introducing water into the interior of the treatment containers enables efficient control of the moisture content of the output material by increasing or reducing its moisture content in such a manner as to obtain a flowable material with the desired moisture level.
Next Patent: RACK PROTECTOR