Method, an arrangement and use of an arrangement of preparing polymer
A method and arrangement of producing polymer comprising polymerizing in reactor having a top zone having a generally conical shape, a middle zone in direct contact with and below said top zone having a generally cylindrical shape, a bottom zone having a generally conical shape thereby polymerizing at least one olefin, in the presence of a polymerization catalyst and fluidization gas to obtain (i) a first stream comprising fluidization gas and particles of olefin polymer, (ii) a second stream comprising fluidization gas and agglomerates of olefin polymer, (iii) a third olefin polymer product stream, —directing the first stream comprising fluidization gas and olefin polymer particles to a series of at least three cyclones connected to the fluidized bed reactor, —separating agglomerates of olefin polymer from the second stream, withdrawing from the fluidized bed polymerization reactor the third olefin polymer product stream.
1. A method of producing polymer particles wherein the method comprises
polymerizing in a fluidized bed polymerization reactor comprising a fluidized bed in the reactor and the reactor having a top zone having a generally conical shape, a middle zone in direct contact with and below said top zone having a generally cylindrical shape, a bottom zone in direct contact with and below the middle zone and having a generally conical shape thereby polymerizing at least one olefin, optionally at least one comonomer and optionally hydrogen, in the presence of a polymerization catalyst and fluidization gas to obtain
(i) a first stream comprising fluidization gas and olefin polymer particles,
(ii) a second stream comprising fluidization gas and agglomerates of olefin polymer,
(iii) a third olefin polymer product stream,
directing the first stream comprising fluidization gas and olefin polymer particles to a series of at least three cyclones connected to the fluidized bed polymerization reactor thereby obtaining from a last cyclone in the series a final stream of fluidization gas depleted of olefin polymer particles and from the at least three cyclones in the series a final stream of olefin polymer particles separated from the fluidization gas,
separating agglomerates of olefin polymer from the second stream comprising fluidization gas and agglomerates of olefin polymer and removing the separated agglomerates from the bottom zone of the fluidized bed polymerization reactor, and
withdrawing from the fluidized bed polymerization reactor the third olefin polymer product stream.
2. The method according to claim 1 wherein the method is for producing polymer particles having a narrow particle size distribution (PSD) in the third olefin polymer product stream.
3. The method according to claim 2 , wherein the narrow particle size distribution (PSD), defined with the span of the particle size distribution as (d 90 -d 10 )/d 50 , of the obtained olefin polymer product in the third olefin polymer product stream is equal to or below 1.5.
4. The method according to claim 1 , wherein in the first stream comprising fluidization gas and olefin polymer particles, the olefin polymer particles have a d 50 value (median particle size) less than 150 μm.
5. The method according to claim 1 , wherein in the second stream comprising fluidization gas and agglomerates of olefin polymer, the agglomerates have d 50 (median particle size) equal to or larger than 25 mm.
6. The method according to claim 1 , wherein the series of at least three cyclones comprises a first cyclone, a second cyclone and a third cyclone and the first cyclone has a separation efficiency from 93 to 99 weight-% of all olefin polymer particles contained in the first stream after the polymerization and/or the second cyclone has a separation efficiency from 98.5 to 99.0 weight-% of all olefin polymer particles contained in the first stream after the polymerization, and/or the third cyclone has a separation efficiency from 99.0 to 99.9 weight-% of all olefin polymer particles contained in the first stream.
7. The method according to claim 1 , further comprising the steps of (a) measuring the mass flow of the polymer in the stream obtained from a cyclone connected in series, (b) determining an average mass flow of polymer in the stream obtained from the last cyclone connected in series based on the measured mass flow over a period of time, and (c) directing the stream obtained from the last cyclone connected in series into the fluidized bed polymerization reactor if the measured mass flow of polymer is at least 20% less than the average mass flow of polymer.
8. The method according to claim 1 , wherein agglomerates of olefin polymer are separated from the fluidization gas and withdrawn from the bottom zone of the reactor by using an agglomerate trap.
9. The method according to claim 2 , wherein the olefin polymer product stream having a narrow particle size distribution is further subjected to post reactor treatment in order to remove unreacted hydrocarbons.
10. The method according to claim 1 wherein the fluidized bed polymerization reactor has no gas distribution grid.
11. An apparatus of producing polymer particles having a narrow particle size distribution (PSD) wherein the apparatus comprises
a fluidized bed polymerization reactor comprising a fluidized bed in the reactor and the reactor having a top zone having a generally conical shape, a middle zone in direct contact with and below said top zone having a generally cylindrical shape, a bottom zone in direct contact with and below the middle zone and having a generally conical shape, for polymerizing at least one olefin, optionally at least one comonomer and optionally hydrogen, in the presence of a polymerization catalyst and fluidization gas to obtain
a first stream comprising fluidization gas and fine particles of olefin polymer,
a second stream comprising fluidization gas and agglomerates of olefin polymer,
a third olefin polymer product stream,
a series of at least three cyclones connected to the fluidized bed polymerization reactor thereby obtaining from a last cyclone in the series a final stream of fluidization gas depleted of fine particles of olefin polymer and a final stream of fine particles of olefin polymer separated from the fluidization gas,
means for separating agglomerates of olefin polymer from the second stream comprising fluidization gas and agglomerates of olefin polymer and means for removing the separated agglomerates from bottom zone of the reactor, and
means for withdrawing the third olefin polymer product stream.
12. A method comprising producing olefin polymer having a narrow particle size distribution with the apparatus of claim 11 .
13. A method according to claim 12 , wherein in the third stream of the obtained olefin polymer product the particle size distribution of the polymer defined as (d 90 -d 10 )/d 50 , is equal to or below 1.5.
14. The method according to claim 3 , wherein the narrow particle size distribution (PSD) of the obtained olefin polymer product in the third olefin polymer product stream is from 1.0 to 1.5.
15. The method according to claim 3 , wherein the narrow particle size distribution (PSD) of the obtained olefin polymer product in the third olefin polymer product stream is from 1.1 to 1.4.
16. The method according to claim 4 , wherein in the first stream comprising fluidization gas and olefin polymer particles, the olefin polymer particles have a d 50 value (median particle size) less than 120 μm.
17. The method according to claim 4 , wherein in the first stream comprising fluidization gas and olefin polymer particles, the olefin polymer particles have a d 50 value (median particle size) less than 80 μm.
18. The method according to claim 13 , wherein in the third stream of the obtained olefin polymer product the particle size distribution of the polymer defined as (d 90 -d 10 )/d 50 , is from 1.0 to 1.5.
19. The method according to claim 13 , wherein in the third stream of the obtained olefin polymer product the particle size distribution of the polymer defined as (d 90 -d 10 )/d 50 , is from 1.1 to 1.4.