Pellet drying and degassing method

Patent metadata

Field	Value
Publication number	US-11549749-B2
Application number	US-201816623579-A
Country	US
Kind code	B2
Filing date	Jun 21, 2018
Priority date	Jun 26, 2017
Publication date	Jan 10, 2023
Grant date	Jan 10, 2023

Abstract

Method for the preparation of dried polymer pellets in a facility having a dryer with a first chamber and a mechanical agitator, and the facility further having a degassing silo with a second chamber, the method includes the steps of guiding a drying gas flow made from or containing a first gas mixture for drying wet polymer pellets into the first chamber, transferring the dried polymer pellets into the second chamber, guiding a second gas mixture for degassing the dried polymer pellets into the second chamber thereby transforming the second gas mixture into a third gas mixture and guiding a portion of the third gas mixture into the first chamber; and process for manufacturing LDPE pellets.

First claim

The invention claimed is:

1. A method for the preparation of dried polymer pellets having a reduced hydrocarbon content in a facility, wherein the pellets are prepared by using an extruder thereby producing polymer strands, and wherein the polymer strands are cut into pellets in an underwater pellet cutter thereby resulting in wet polymer pellets,
the facility having a dryer with a first chamber having an upper and a lower end having a first polymer inlet, a first polymer outlet above the first polymer inlet, a first gas inlet at the upper end, a first gas outlet below the first gas inlet and a mechanical agitator, and
the facility further having a degassing silo with a second chamber having a second polymer inlet, a second polymer outlet, a second gas inlet, and a second gas outlet,
the method comprising the steps:
i) guiding a drying gas flow comprising a first gas mixture through the first gas inlet into the first chamber,
ii) inserting the wet polymer pellets through the first polymer inlet into the first chamber,
iii) drying the wet polymer pellets in a countercurrent provided by the drying gas flow and by using the mechanical agitator, thereby yielding dried polymer pellets,
iv) transferring the dried polymer pellets through the first polymer outlet and the second polymer inlet into the second chamber,
v) guiding a second gas mixture through the second gas inlet into the second chamber,
vi) degassing the dried polymer pellets using the second gas flow, thereby transforming the second gas mixture into a third gas mixture comprising hydrocarbons, and
vii) guiding a portion of the third gas mixture into the first chamber,
wherein the wet polymer pellets inserted into the first chamber in step ii) have a temperature of from 20° C. to 80° C. and the second gas mixture guided into the second chamber in step v) have a temperature of from 20° C. to 80° C. and
wherein the dried polymer pellets having a reduced hydrocarbon content are withdrawn from the second chamber through the second polymer outlet and the dried polymer pellets withdrawn through the second polymer outlet have a temperature which is from 0.1° C. to 20° C. higher than the temperature of the second gas mixture guided into the second chamber.

2. The method of claim 1 , wherein the portion of the third gas mixture forms the first gas mixture and is guided through the first gas inlet into the first chamber, or
wherein the portion of the third gas mixture does not form the first gas mixture, but is added to the drying gas flow of the first gas mixture and is guided through the first gas inlet into the first chamber, or
wherein the first chamber has a third gas inlet spaced apart from the first gas inlet and the portion of the third gas mixture is guided through the third gas inlet into the first chamber.

3. The method of claim 1 , wherein the polymer pellets are polyolefin pellets.

4. The method of claim 1 , wherein the polymer pellets comprise low density polyethylene.

5. The method of claim 1 , wherein the facility comprises a first separation unit having a separation sieve, wherein agglomerates are removed using the separation sieve prior to insertion of the wet polymer pellets into the first chamber.

6. The method of claim 5 , wherein the first separation unit is placed adjacent to the first chamber being at least partially at the same height as the first gas outlet or as the first polymer outlet.

7. The method of claim 1 , wherein
the drying gas flow becomes wet during the drying process and the resulting wet gas mixture is guided through the first gas outlet to a cyclone separator and through the cyclone separator to at least one suction fan,
wherein the cyclone separator removes remaining polymer pellets, other particles or condensed fluid droplets,
wherein the suction fan evacuates the wet gas from the first chamber and though the cyclone separator.

8. The method of claim 1 , wherein the first gas flow, the third gas flow, or both are heated prior to being guided into the first chamber using a first heating unit.

9. The method of claim 8 , wherein the first heating unit is a steam-operated heater.

10. The method of claim 1 , wherein the wet pellets are conveyed by process water of an underwater pellet cutter, for inserting into the first chamber in accordance with step ii).

11. The method of claim 1 , wherein the first, second and third gas mixtures predominantly contain nitrogen, oxygen, or both.

12. The method of claim 1 , wherein the first gas inlet is arranged centrally at the upper end, thereby the drying gas flow is directed towards the opposing bottom end.

13. A process for manufacturing LDPE-pellets in an industrial plant, the industrial plant having a reactor for polymerization reactions, an extruder and a facility,
the facility having a dryer with a first chamber having an upper and a lower end having a first polymer inlet, a first polymer outlet above the first polymer inlet, a first gas inlet at the upper end, a first gas outlet below the first gas inlet and a mechanical agitator, and
the facility further having a degassing silo with a second chamber having a second polymer inlet, a second polymer outlet, a second gas inlet, and a second gas outlet,
the process comprising the steps:
a) polymerizing ethylene in the reactor at a temperature of 140 to 320° C. and a pressure of 1400 to 3200 bar, thereby yielding a LDPE polymer,
b) separating the LDPE polymer and ethylene and recycling unreacted ethylene,
c) extruding the LDPE polymer to obtain a homogenized LDPE melt,
d) pelletizing the LDPE melt to obtain wet LDPE pellets using an underwater pellet cutter, and
e) drying and degassing the wet LDPE pellets using the method of claim 1 .

14. A process for manufacturing LDPE-pellets in an industrial plant,
the industrial plant having a reactor for polymerization reactions, an extruder and a facility,
the facility having a dryer with a first chamber having an upper and a lower end having a first polymer inlet, a first polymer outlet above the first polymer inlet, a first gas inlet at the upper end, a first gas outlet below the first gas inlet and a mechanical agitator, and
the facility further having a degassing silo with a second chamber having a second polymer inlet, a second polymer outlet, a second gas inlet, and a second gas outlet,
the process comprising the steps:
a) polymerizing ethylene in the reactor at a temperature of 140 to 320° C. and a pressure of 1400 to 3200 bar, thereby yielding a LDPE polymer,
b) separating the LDPE polymer and ethylene and recycling unreacted ethylene,
c) extruding the LDPE polymer to obtain a homogenized LDPE melt,
d) pelletizing the LDPE melt to obtain wet LDPE pellets using an underwater pellet cutter,
e.i) guiding a drying gas flow comprising a first gas mixture through the first gas inlet into the first chamber,
e.ii) inserting wet polymer pellets through the first polymer inlet into the first chamber,
e.iii) drying the wet polymer pellets in a countercurrent provided by the drying gas flow and by using the mechanical agitator, thereby yielding dried polymer pellets,
e.iv) transferring the dried polymer pellets through the first polymer outlet and the second polymer inlet into the second chamber,
e.v) guiding a second gas mixture through the second gas inlet into the second chamber,
e.vi) degassing the dried polymer pellets using the second gas flow and thereby transforming the second gas mixture into a third gas mixture comprising hydrocarbons, and
e.vii) guiding a portion of the third gas mixture into the first chamber,
wherein the wet polymer pellets inserted into the fi

Assignees

• Basell Polyolefine Gmbh

Inventors

• Mei Giulia
• Mohrbutter Juergen
• Littmann Dieter
• Wolf Christoph
• Finette Andre-Armand
• Deuerling Michael
• Penzo Giuseppe

Classifications

• B29K2023/0633

  LDPE, i.e. low density polyethylene · CPC title

• B29B9/065

  under-water, e.g. underwater pelletizers · CPC title

• B29B13/065 Primary

  of powder or pellets · CPC title

• F26B5/08

  by centrifugal treatment · CPC title

• B29K2105/251

  Particles, powder or granules (expandable particles B29K2105/046) · CPC title