Patent Application
20090090019
The present invention relates to a treatment unit for granular material having a heat-regeneration group.
In the description and the claims of the present invention, the term “granular” means both materials that are classified as such by being naturally made of granules and those obtained by a milling process (such as those known as re-milled products) and powders.
There is often the need of performing operations, such as dehumidification or drying of granular materials, on specific granules of plastic materials, before being used in a moulding press in order to make them suitable for successive treatment and/or processing operations.
To perform such operations, a granular material is loaded into and kept in silos, also called “hoppers”, for a predetermined time. A hot and dehumidified gas medium, such as dry hot air or inert gas, typically nitrogen, is caused to flow through them.
After flowing through the granular material in a silo, the gas medium is collected and recycled after having been filtered and heated/dehumidified in order giving it features of humidity, temperature, etc. required for that specific granular material to be treated.
Granular material dehumidifying plants have already been proposed where, the employed gas medium leaving a dehumidification silo or hopper is conveyed trough a suitable duct to a remote, i.e. relatively far from the silo, heat exchanger for recovering its residual heat, and thus for being cooled.
When granules of plastic material need to be treated in hoppers or silos, the treatment gas medium (air) is supplied to a lower area of the silo so that the gas medium is caused to flow throughout the entire useful height of the silo, and thus to hit practically all the material in it, so as to perform forced dehumidification and preheating of the granular material that will, consequently, be used in optimum conditions for subsequent processing.
The processing air at the outlet of a treatment hopper is charged with humidity and still possesses a considerable amount of heat that is usually employed to pre-heat the processing air to be supplied to the hopper through dehumidification equipments. Thus, cooling of the air coming out form the hopper is also obtained, and in view of the fact that the air flow coming out from the hopper, as known, has to be conveyed first to a pressurization unit (such as a blower) and then to a water adsorbing unit, this is advantageous for optimum working of both such units.
In conventional plants heat exchange between air coming from the hopper and air to be conveyed to the same hopper usually occurs in counter-current fashion in a suitable externally located heat-exchanging group.
A plant of this type, however, involves considerable heat dispersion, which takes place at least in the connecting ducts between hopper and heat-exchanging group and cannot be reduced below certain limits even by providing good insulating materials around the connecting ducts. In any case, such a plant requires a very large plant volume and suitable support structures for both the silo or hopper and the heat-exchanging group.
The first aim of the present invention is to provide a treatment unit for granular materials and particularly plastic granular materials that are suitable for eliminating or drastically reducing the drawbacks mentioned above in connection with the conventional granular materials treatment plants.
Another object of the present invention is to provide a granular material treatment unit which can operate in optimum conditions for both the dehumidification processing of granular material and the heat regeneration from the gas medium used for processing the granular material.
Another object of the present invention is to provide a compact treatment unit obtainable at competitive manufacturing costs.
Still another object of the resent invention is to provide a dehumidification and/or drying plant designed for correctly perform treatment operations on granular materials at a lower energy consumption than with conventional plants.
According to a first aspect of the present invention here is provided a treatment unit for a granular material, the treatment unit comprising:
The treatment unit further comprises:
According to another aspect of the present invention, a dehumidification plant for granular material is also provided, comprising:
Further aspects and advantages of the present invention will more clearly appear from the following detailed description of specific embodiments of a granular material treatment unit, the description being given with reference to the accompanying drawings, in which:
In the accompanying drawings, the same or similar parts or components have been indicated with the same reference numerals.
With reference to the above mentioned Figures, a treatment unit 1 for granular materials, such as granular plastic materials, is shown which comprises a support structure S, a silo or hopper 2 which delimits a receiving cavity 3 for at least one granular material which is supplied through a loading mouth 4 and exits through a granular material discharging or delivery mouth 5, the latter being located in a lower area of the silo 2.
Feeding means of at least one treatment gas medium, e.g. air or an inert gas, such as nitrogen, are also provided internally and specifically at a heat-exchanging group. An outlet or a plurality of outlets for the gas medium is provided at the top of the treatment unit. According to the illustrated embodiment, the feeding means comprise a feeding pipe or duct 6, e.g. an ell member, which from the top of the silo extends downwards to a lower zone of the silo where it is in fluid communication with a dispenser 6a of treatment gas medium.
The treatment unit further comprises a heat exchanging group 8 which can be secured at the top of cavity 3 and arranged to partly close it.
More particularly, the heat exchanging group 8 comprises:
The plurality of ducts and chamber 10 are thus arranged in heat exchange relationship.
Advantageously, ducts 9 are arranged to deliver a treatment gas medium therein from cavity 3 to a manifold area 11 provided between the heat-exchanging group 8 and a top roof plate 12, which is in fluid communication with the outside through a duct 12a having an annular cross section.
The heat-exchanging group 8 preferably comprises two substantially identical walls or plate elements, i.e. a base wall 8a and a top wall 8b, respectively, which have a ring configuration and are connected to one another through an outer side wall or jacket 8c, possibly wound by a layer of a heat insulating or lagging material 8d. Each ring wall delimits a central circular opening into which a granular material feeding duct 13 of can be inserted that extends to loading mouth 4.
A plurality of bores F are provided in the plate elements 8a, 8b so that each bore on a plate element 8a, 8b is substantially in line with a bore on the other plate element 8b, 8a, respectively, and thus each duct 9 is fitted into two aligned bores each formed in a respective plate element 8a, 8b.
Sealing between ducts and plate elements is ensured by arranging respective annular joint sealing elements 14, e.g. made of a thermoplastic material such as Santoprene® (registered trademark of Advanced Elastomer Systems, L.P.) along the edge of each bore before assembling any duct 9.
The inlet opening 10a and the outlet opening 10b for gas medium are provided, instead, by inserting and securing, e.g. through welding, a respective sleeve collar into bores formed in the jacket or side wall 8c.
According to a preferred embodiment of the invention, a filtering group 15 for the gas medium is located, in use, immediately below the heat exchanging group and can be secured either to silo 2 or to the plate element or base wall 8b.
As it is known in the art, silo 2 can comprise, in use, a lower portion having a configuration of a truncated cone 2a, and an intermediate substantially cylindrical portion 2b (located at the same level as the dispenser 6a). Moreover, a layer of heat-insulating or lagging material 2c can be provided on silo 2.
The treatment unit according to the present invention can be employed in a plant for processing granular materials, such as granular plastic materials, as illustrated in
Such a plant comprises a treatment unit 1 for granular materials, a filter 16 designed to receive the air that comes out of the top of the treatment unit 1 and is then conveyed to a dryer 17, where it is dehumidified and then supplied to chamber 10 for being pre-heated. The pre-heated air is first supplied to a heater or heating means 18 and then to the feeding means 6 for being again fed to the receiving cavity 3 for heating and dehumidifying the granular material contained therein.
It will be understood that in order to convey the gas medium to the apparatuses and the ducts in a plant according to the present invention, compression means (e.g. a blower) can be employed, while possibly supplying the gas medium at a relatively high pressure to the plant, monitoring the pressure thereof during the processing steps and, if necessary, energizing the pressurizing means when the pressure becomes lower than a predetermined level.
According to such a plant, the still hot air leaving the receiving cavity is loaded with humidity that was absorbed while flowing through the granular material, releases a good deal of its enthalpy while pre-heating the processing fluid coming from the dryer 17. The required power required for heating the processing gas medium, i.e. the air to be fed to the hopper, by means of an electrical resistance or heater 18 in order to heat it to a predetermined temperature suitable for processing a granular material will then be certainly lower than that required with the solutions proposed up to now. The air discharged from the hopper, on the other hand, has already been partly cooled down due to heat exchanged with the processing gas medium (air to be conveyed to the hopper), and thus another heat-exchanger could be no longer necessary for the cooling thereof, and the air can then be again conveyed to the dryer, possibly after flowing through filter 16.
By providing a treatment unit with an heat-exchanging group mounted at the top of the receiving cavity, heat dispersions at the connections between hopper and heat-exchanger, which necessarily occur with the solutions proposed up to now, are eliminated or at least drastically reduced. At the same time, air blown into the receiving chamber is at an higher temperature than that of the air coming from the hopper and conveyed to heat-exchangers according to the state of the art teachings. The heat exchanger efficiency is, therefore, higher than that of solutions proposed up to now and a greater heat regeneration is also obtained.
It should also be noted that inspection and maintenance operations of a treatment unit according to the present invention are very easily conducted, as all the components thereof can be fully disassembled.
According to the present invention, ducts having a large cross-section and thus do not clog easily and do not require a thorough air filtration are provided, and thus low powered filtering means can be adopted.
Moreover, by ensuring a watertight seal as described above, owing to the provision of thermoplastic material rings, the treatment unit is not affected by the negative effects caused by thermal expansion mainly in the axial direction of each duct, whereas in conventional heat-exchangers where tubes are welded, welding resistance could be drastically impaired when temperatures of fluids to be heated/cooled change on a large scale.
It should also be noted that the air temperature coming from the treatment unit is lower than that of the air coming from hoppers in conventional treatment plants, and this results in an improvement of security for operators inspecting the plant, particularly in the upper part of the hopper.
The treatment unit as above described is susceptible to numerous modifications and variations within the scope of the invention as defined by the claims.
Thus, for example, hoppers or silos having a squared or polygonal cross-section can be employed.
In so far as the heat-exchanging group geometry is concerned, it should be understood that any known measure in the art can be adopted, in particular if directed toward improving convection and overall heat exchange coefficients. For example, one could provide:
| Number | Date | Country | Kind |
|---|---|---|---|
| VR2007A000140 | Oct 2007 | IT | national |
