Pellet drying and degassing method

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 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• wherein the dried polymer pellets having a reduced hydrocarbon content are withdrawn from the second chamber through the second polymer outlet and the dried polymer pellets withdrawn through the second polymer outlet have a temperature which is from 0.1° C. to 20° C. higher than the temperature of the second gas mixture guided into the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.