Reactor assembly and method for polymerization of olefins

1. A method for polymerizing olefins in a fluidized bed reactor, wherein a fluidized bed is formed by polymer particles in an upwards rising fluidization gas, said upwards rising fluidization gas has a superficial velocity in a middle zone of from 0.05 to 0.8 m/s, said method comprising the steps of:

(i) withdrawing a fluidization gas stream via an outlet from said fluidized bed reactor at a height of more than 90% of the total height of said fluidized bed reactor;

(ii) separating polymer particles from said fluidization gas stream to produce an overhead stream and a solid recycling stream;

(i) branching off from said solid recycling stream a stream to downstream process stages;

(iv) directing said stream to downstream process stages to downstream process stages; and

(v) recycling the solid recycling stream into said fluidized bed reactor;

wherein said fluidized bed reactor comprises a bottom zone, said middle zone and an upper zone, an equivalent cross-sectional diameter of the bottom zone being monotonically increasing with respect to the flow direction of the fluidization gas through the fluidized bed reactor and an equivalent cross-sectional diameter of the upper zone being monotonically decreasing with respect to the flow direction of the fluidization gas through the fluidized bed reactor; and

wherein there is an unobstructed passageway in the direction of flow of the fluidization gas through the fluidized bed reactor from the bottom zone to the upper zone; and

the reactor further comprises an outlet for the polymer whereby the polymer stream withdrawn from the fluidized bed reactor via outlet of the polymer and the solid recycling stream branched off to the output of the polymer are combined for product recovery; and

the reactor further comprising gas/solid separation means, a flow through device, a solid recycling line, a solid recycling inlet, a gas circulation line, an inlet for fluidization gas located in the bottom zone and a controller, the method further comprising the steps of:

a) measuring the mean particle size and/or the particle size distribution and/or the concentration of all solids of an fluidization gas stream from the fluidized bed reactor;

b) analyzing the operation conditions in the fluidized bed reactor;

c) sending the data obtained in steps a) and b) to a controller;

d) processing the data by the controller; and

e) adjusting the flow through device by the controller;

whereby the flow through device varies the solid recycling stream via solid recycling line back to the fluidized bed reactor.

2. The method according to claim 1 , wherein the fluidized bed reactor further comprises a flow through device, the flow through device branches off from the solid recycling stream entering the flow through device a stream to downstream process stages directed to down stream process stages through the line to downstream process stages.

3. The method according to claim 1 , wherein the fluidized bed reactor further comprises one or more outlets for fluidization gas streams located in the upper zone.

4. The method according to claim 1 , wherein said fluidized bed reactor comprises no gas distribution grid and/or plates.

5. The method according to claim 1 , wherein the gas solids/separation means are cyclones.

6. The method according to claim 1 , wherein the outlet of the polymer is located in the middle zone.

7. Method according to claim 1 , wherein step b) comprises the measurement of fluidization velocity, u f .

8. Method according to claim 1 , furthermore comprising the steps of:

dd) predicting the mean particle size and/or the particle size distribution of the fluidization gas stream using the data obtained in step b);

de) comparing the measured and the predicted mean particle size and/or the particle size distribution of the fluidization gas stream of steps a) and dd).

9. Method according to claim 1 , whereby the solid recycling stream is increased when the content of fines deduced from the measured particle size distribution of step a) is larger than a predetermined set point for the content of fines.

10. Method according to claim 1 , wherein the flow through device varies the solid recycling stream back to the fluidized bed reactor and/or allows a stream to downstream process stages.

11. Method according to claim 1 , wherein said fluidization gas is upwards rising fluidization gas and said upwards rising fluidization gas has a superficial velocity in the middle zone of from 0.05 to 0.8 m/s.

12. A reactor assembly for the production of polymers including a fluidized bed reactor comprising a bottom zone, a middle zone and an upper zone, one or more outlets for fluidization gas streams located in the upper zone, gas/solid separation means, a flow through device, a solid recycling line, a solid recycling inlet, a gas circulation line, an inlet for fluidization gas located in the bottom zone;

the outlet for the fluidization gas stream being coupled with the fluidized bed reactor via a gas/solid separation means, the gas circulation line and the inlet and via the solid recycling line, the gas/solid separation means and the solid recycling inlet;

an equivalent cross-sectional diameter of the bottom zone being strictly monotonically increasing with respect to a flow direction of the fluidization gas through the fluidized bed reactor; and

wherein there is an unobstructed passageway in the direction of flow of the fluidization gas through the fluidized bed reactor from the bottom zone to the upper zone,

characterized in that the solid recycling line includes the flow through device,

wherein the flow through device allows for varying the amount of a stream of particles, gas or fluid or mixtures thereof flowing through the device whereby the variation occurs by adjusting the flow through device and the flow through device lets pass 0 to 100% of a stream in a certain direction and the flow through device allows for passing the rest 100 to 0% of the stream in at least one additional direction, and

the gas/solids separation means are cyclones.

13. The reactor assembly according to claim 12 , wherein said fluidized bed reactor comprises no gas distribution grid and/or plates.