Process and apparatus for removing polymer material from a gas-solids olefin polymerization reactor

1. A process for removing polymer material from a gas-solid olefin polymerization reactor wherein the gas-solid olefin polymerization reactor is connected to a top part of an outlet vessel via a feed pipe, the process comprising the steps of:

(i) discharging polymer material from the gas-solid olefin polymerization reactor via the feed pipe into the outlet vessel;

(ii) establishing a powder surface of discharged polymer material within the outlet vessel in a section of a middle part of the outlet vessel;

(iii) injecting barrier gas through a barrier gas injection point in a section of a bottom part of the outlet vessel below the powder surface;

(iv) recovering polymer material from the outlet vessel through a vessel outlet in a section below the barrier gas injection point;

characterized in that

the powder surface and the barrier gas injection point are situated in the outlet vessel as such to fulfill the following criteria:

R′=X/Y≤ 2.0;

and

R″=X/D≥ 1.0;

wherein X=Distance between the powder surface and the barrier gas injection point; Y=Distance between the barrier gas injection point and the vessel outlet; and D=Equivalent outlet vessel diameter.

2. The process of claim 1 , wherein the powder surface is established by extending the feed pipe into the middle part of the outlet vessel to form a dip tube and the powder surface is established at the lower end of the dip tube.

3. The process of claim 2 , wherein the lower end of the dip tube is situated within the middle part of the outlet vessel as such to fulfill the following criterion:

R′″=W/L= 0.1 to 0.5;

wherein W=Distance between the top part of the outlet vessel and the lower end of the dip tube; and L=Distance between the top part of the outlet vessel and the vessel outlet equivalent to the total vertical length of the outlet vessel.

4. The process of claim 1 , wherein the polymer material is discharged from the gas-solid olefin polymerization reactor with a velocity of at least 5 cm/s.

5. The process of claim 1 , wherein the ratio of the flow rate of the barrier gas to the flow rate of the entrained gas mixture in the polymer material recovered in step (iv) in volumetric basis is from 0.5 to 2.5.

6. The process of claim 1 , wherein the ratio of the flow rate of the barrier gas to the flow rate of the entrained gas mixture in the polymer material recovered in step (iv) in volumetric basis is from 0.8 to 2.0.

7. The process of claim 1 , wherein the ratio of the flow rate of the barrier gas to the flow rate of the entrained gas mixture in the polymer material recovered in step (iv) in volumetric basis is from 1.0 to 1.8.

8. The process of claim 1 , wherein the ratio of the flow rate of the barrier gas to the flow rate of the entrained gas mixture in the polymer material recovered in step (iv) in volumetric basis is from 1.0 to 1.5.

9. The process of claim 1 further comprising the step of recovering gas from the top part of the outlet vessel and returning said gas to the gas-solid olefin polymerization reactor through return gas pipe.

10. The process of claim 1 , wherein the polymer material is selected from alpha-olefin homo- or copolymers having alpha-olefin monomer units of from 2 to 12 carbon atoms.

11. The process of claim 1 , wherein the barrier gas is selected from inert gas or fluidization gas.

12. The process of claim 1 , wherein the barrier gas efficiency, being the percentage of the entrained gas mixture, escaped from the gas-solids olefin polymerization reactor through the vessel outlet, that can be displaced by the barrier gas, is at least 75%.

13. An apparatus for continuously removing polymer material comprising

a gas-solids olefin polymerization reactor, an outlet vessel and a feed pipe connecting the gas-solids olefin polymerization reactor with a top part of the outlet vessel, wherein the outlet vessel comprises

means for establishing a powder surface of discharged polymer material within the outlet vessel in a section of a middle part of the outlet vessel;

a barrier gas injection point in a section of a bottom part of the outlet vessel below the powder surface, and

a vessel outlet in a section below the barrier gas injection point;

characterized in that

the powder surface and the barrier gas injection point are situated in the outlet vessel as such to fulfill the following criteria:

R′=X/Y≤ 2.0;

and

R″=X/D≥ 1.0;

wherein X=Distance between the powder surface and the barrier gas injection point; Y=Distance between the barrier gas injection point and the vessel outlet; and D=Equivalent outlet vessel diameter.

14. The apparatus of claim 13 , wherein the means for establishing the powder surface comprises a dip tube that extends from the feed pipe into the middle part of the outlet vessel and the powder surface is established at the lower end of the dip tube.

15. The apparatus of claim 14 , wherein the lower end of the dip tube is situated within the middle part of the outlet vessel as such to fulfill the following criterion:

R′″=W/L= 0.1 to 0.5;

wherein W=Distance between the top part of the outlet vessel and the lower end of the dip tube; and L=Distance between the top part of the outlet vessel and the vessel outlet equivalent to the total vertical length of the outlet vessel.

16. The apparatus of claim 13 further comprising a return gas pipe connecting the top part of the outlet vessel and the gas-solid olefin polymerization reactor.

17. A polymerization method comprising:

polymerizing alpha-olefin homo- or copolymers having alpha-olefin monomer units of from 2 to 12 carbon atoms in the apparatus of claim 13 .

18. A method for increasing a barrier gas efficiency of a gas-solids olefin polymerization reactor to at least 75% comprising:

polymerizing alpha-olefin homo- or copolymers having alpha-olefin monomer units of from 2 to 12 carbon atoms in the apparatus of claim 13 .