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EP-4229345-B1 - PLANT FOR DRYING GRANULAR POLYMERIC MATERIAL

EP4229345B1EP 4229345 B1EP4229345 B1EP 4229345B1EP-4229345-B1

Inventors

  • PIVA, RINALDO

Dates

Publication Date
20260506
Application Date
20211015

Claims (15)

  1. A plant (1) for drying granular polymer material, comprising a hopper (2), in which granular polymer material is dried, and a process gas circuit (10), which is configured to supply a process gas to the hopper (2) in order to dry the granular polymer material, wherein the process gas circuit (10) comprises: - a dehumidification and heating unit (20) which is configured to dehumidify and heat the process gas to predefined humidity and temperature values for supply to the hopper (2), respectively, - a purification group (3) which is positioned at the outlet from the hopper (2) and upstream of the dehumidification and heating unit (20) and which is configured to purify the process gas from contaminating substances which are released by the granular polymer material in the hopper (2), and - a cyclone separator (6) which is positioned at the outlet from the hopper (2) and upstream of the purification group (3), and which is configured to separate a dust of the polymer material granules from the process gas being introduced into the purification group, wherein the purification group (3) comprises - a condenser (32) which is configured to cool the process gas to a predefined condensation temperature of the contaminating substances so as to separate from the process gas the contaminating substances condensed in this manner, - a filter (33) which is positioned at the outlet from the condenser (32) and which contains activated carbon capable of absorbing non-condensed contaminating substances.
  2. A plant (1) according to claim 1, wherein the condenser (32) is configured to cool the process gas to a temperature between 10°C and 30°C.
  3. A plant (1) according to claim 1, wherein the condenser (32) is configured to cool the process gas to a temperature between 15°C and 25°C.
  4. A plant (1) according to claim 1, wherein the condenser (32) is configured to cool the process gas to a temperature of substantially 20°C.
  5. A plant (1) according to any one of the preceding claims, wherein the purification group (3) comprises a first pipe (34) for the process gas which is being discharged from the hopper (2) and upstream of the condenser (32), a second pipe (35) for the process gas which is being discharged from the filter (33) and upstream of the dehumidification and heating unit (20), and a heat exchanger (31) which includes the first pipe (34) and second pipe (35), the heat exchanger (31) being configured to exchange heat between the process gas being introduced into the purification group (3) through the first pipe (34) and the process gas being discharged from the purification group (3) through the second pipe (35).
  6. A plant (1) according to any one of the preceding claims, wherein the process gas circuit (10) comprises a movement unit (30) which is configured to move the process gas along the process gas circuit (10) between the dehumidification and heating unit (20), the hopper (2) and the purification group (3), and furthermore in the purification group (3) between the heat exchanger (31), the condenser (32) and the filter (33).
  7. A plant (1) according to any one of the preceding claims, wherein the process gas circuit (10) is a closed circuit.
  8. A plant (1) according to any one of the preceding claims, wherein downstream of the dehumidification and heating unit (20) there is provided an inlet pipe (11), by means of which the process gas is introduced into the hopper (2), along the inlet pipe (11) there being provided a sampling location (12) for sampling the process gas.
  9. A plant (1) according to any one of the preceding claims, wherein downstream of the dehumidification and heating unit (20) there is provided an inlet pipe (11), by means of which the process gas is introduced into the hopper (2), at the end of the inlet pipe (11) there being mounted a diffuser which is introduced into the granular polymer material contained in the hopper (2).
  10. A plant (1) according to any one of the preceding claims, wherein there is provided a bypass valve of the process gas which allows the purification group (3) to be excluded from the process gas circuit (10).
  11. A plant (1) according to any one of the preceding claims, wherein the filter (33) comprises a plurality of filtering elements which contain activated carbon.
  12. A plant (1) according to claim 11, wherein the filtering elements are cylindrical.
  13. A plant (1) according to any one of the preceding claims, wherein the condenser (32) is connected to a cooling water line (16).
  14. A plant (1) according to any one of the preceding claims, wherein the process gas circuit (10) comprises a movement unit (30), comprising one or more blowers, in order to move the process gas along the process gas circuit (10).
  15. A plant (1) according to any one of the preceding claims, wherein the movement unit (30) is connected downstream of the cyclone separator (6) with respect to the process gas flow.

Description

Technical field The present invention relates to a plant for drying granular polymer material. Technological background The invention is particularly used in industrial processes for converting plastics material into granules by means of extrusion or moulding. It is known that such operations require, in order to ensure an adequate level of quality of the moulded product, that the plastics material which is introduced into the moulds have as much humidity removed as possible. However, this requirement is not very compatible with the high levels of hygroscopic properties of some plastics materials which are increasingly used in the field, such as, for example, those based on recycled polyethylene terephthalate (rPET). Therefore, these plastics materials, before being subjected to the extrusion or moulding process, have to be advantageously processed in suitable drying plants where the content of water of the granules is reduced to the minimal quantities required by the conversion process. In a commonly used process, the drying of the granular polymer material is carried out inside a hopper, in which the material to be dried is placed and in which there is introduced a continuous flow of a process gas which is hot and dry and which, by coming into contact with the granular material, provides for stripping the water present in the granules. The process gas, which is typically air, before being introduced into the hopper in order to come into contact with the granular material to be dried, is dehumidified in a suitable dehumidification unit and is subsequently heated to the desired temperature. In a known example of a drying plant, the process gas being discharged from the hopper is placed back into circulation in order to be dehumidified, heated and reintroduced into the hopper again. A main disadvantage of this prior art is that the resin loaded in the hopper and the process gas which is blown in through the resin contain some contaminating substances, such as, for example, residues of benzene and relevant derivatives, acetaldehyde (AA) and possible residual oils resulting from the recovery cycle of the recycled PET. It is evident that these contaminating substances present in the plastics material which is introduced into the moulds irreparably compromise the quality level of the moulded product. The market requires increasing quantities of rPET and the quality of the rPET tends to be worse and worse, therefore, the search for solutions which allow a reduction in the chemical impurities in the plastics material constitutes a requirement which is particularly felt in the technical field in question. DE 197 57 537 A1 discloses a plant for drying granular polymer material. Statement of invention The problem addressed by the present invention is to provide a drying plant which is structurally and functionally configured to at least partially overcome one or more of the disadvantages set out above with reference to the cited prior art. In particular, an object of the present invention is to provide a drying plant which reduces the chemical impurities of the plastics materials with respect to a conventional drying plant as described above with reference to the prior art. An object of the present invention is also to provide a drying plant which reduces the overall emission of polluting substances with respect to a conventional drying plant as described above with reference to the prior art. Furthermore, an object of the present invention is to provide a drying plant which has a greater level of energy efficiency with respect to a conventional drying plant as described above with reference to the prior art. Another object of the invention is to provide a drying plant which is simple to construct and carry out. The problem and the objects indicated above are solved and overcome by the present invention by means of a drying plant comprising one or more of the features of the appended claims. In a first aspect thereof, the invention is directed towards a plant for drying granular polymer material, comprising a hopper, in which the granular polymer material is dried, and a process gas circuit, which is configured to supply a process gas to the hopper in order to dry the granular polymer material. The process gas circuit comprises a dehumidification and heating unit which is configured to dehumidify and heat the process gas to predefined humidity and temperature values for supply to the hopper, respectively. The process gas circuit further comprises a purification group which is positioned at the outlet from the hopper and upstream of the dehumidification and heating unit and which is configured to purify the process gas from contaminating substances which are released by the granular polymer material in the hopper. The purification group comprises a condenser which is configured to cool the process gas to a predefined condensation temperature of the contaminating substances so as to separate from the process gas the co