Polyethylene production with multiple polymerization reactors

Patent metadata

Field	Value
Publication number	US-9556283-B2
Application number	US-201414339277-A
Country	US
Kind code	B2
Filing date	Jul 23, 2014
Priority date	May 21, 2010
Publication date	Jan 31, 2017
Grant date	Jan 31, 2017

Abstract

A system and method for discharging a transfer slurry from a first polymerization reactor through a transfer line to a second polymerization reactor, the transfer slurry including at least diluent and a first polyethylene. A product slurry is discharged from the second polymerization reactor, the product slurry including at least diluent, the first polyethylene, and a second polyethylene. The velocity, pressure drop, or pressure loss due to friction in the transfer line is determined, and a process variable adjusted in response to the velocity, pressure drop, or pressure loss not satisfying a specified value.

First claim

What is claimed is:

1. A method of operating a polyethylene reactor system, comprising:
discharging continuously a transfer slurry from a first polymerization reactor through a first transfer line to a second polymerization reactor, the transfer slurry comprising diluent and a first polyethylene;
discharging a product slurry from a second polymerization reactor, the product slurry comprising diluent, the first polyethylene, and a second polyethylene;
calculating, during operation of the system, a pressure loss in the first transfer line by,
determining a flow rate of the transfer slurry,
calculating a velocity of the transfer slurry as a function of the flow rate,
determining a density of the transfer slurry,
calculating a Reynolds Number of the transfer slurry in the first transfer line as a function of the velocity, the density, a viscosity of the transfer slurry, and an internal diameter of the first transfer line, and
determining a friction factor of an internal surface of the first transfer line as a function of the Reynolds number and a surface roughness to diameter ratio of the internal surface,
wherein the calculated pressure loss is a function of the friction factor, a length to internal diameter ratio of the first transfer line, the density, and the velocity; and

measuring, during operation of the system, a pressure differential through the first transfer line to determine a measured pressure differential and adjusting a process variable in response to the measured pressure differential exceeding the calculated pressure loss by a specified amount,
wherein the adjusting of the process variable comprises increasing and/or allowing pressure to increase in the first polymerization reactor, lowering slurry viscosity in the first polymerization reactor, lowering pressure in the second polymerization reactor, or placing in service a second transfer line and discharging continuously at least a portion of the transfer slurry from the first polymerization reactor through the second transfer line to the second polymerization reactor.

2. The method of claim 1 , wherein the first polymerization reactor and the second polymerization reactor each comprise a liquid-phase reactor.

3. The method of claim 1 , wherein the first polymerization reactor and the second polymerization reactor each comprise a loop reactor.

4. The method of claim 1 , further comprising:
feeding ethylene, diluent, and catalyst to the first polymerization reactor;
polymerizing ethylene in the first polymerization reactor to form the first polyethylene, wherein the transfer slurry comprises active catalyst; and
polymerizing ethylene in the second polymerization reactor to form the second polyethylene.

5. The method of claim 1 , further comprising feeding diluent to the second polymerization reactor.

6. The method of claim 1 , further comprising feeding a comonomer to the first polymerization reactor and/or to the second polymerization reactor.

7. The method of claim 6 , wherein the comonomer comprises propylene, butene, 1-pentene, 1-hexene, 1-octene, and/or 1-decene.

8. The method of claim 1 , further comprising feeding hydrogen to the first polymerization reactor and/or to the second polymerization reactor.

9. The method of claim 1 , wherein the adjusting of the process variable comprises the increasing of the pressure and/or the allowing of the pressure to increase in the first polymerization reactor.

10. The method of claim 9 , wherein the increasing of the pressure in the first polymerization reactor comprises increasing diluent feed pressure to the first polymerization reactor.

11. The method of claim 1 , wherein the adjusting of the process variable comprises the lowering of the slurry viscosity in the first polymerization reactor.

12. The method of claim 11 , wherein the lowering of the slurry viscosity comprises increasing diluent feed rate to the first polymerization reactor, decreasing solids concentration in the first polymerization reactor, and/or increasing temperature in the first polymerization reactor.

13. The method of claim 1 , wherein the adjusting of the process variable comprises the lowering of the pressure in the second polymerization reactor.

14. The method of claim 13 , wherein the lowering of the pressure in the second polymerization reactor comprises increasing an open position of a flow control valve through which the product slurry discharges from the second polymerization reactor.

15. The method of claim 1 , wherein the adjusting of the process variable comprises the placing in service the second transfer line and discharging continuously at least a portion of the transfer slurry from the first polymerization reactor through the second transfer line to the second polymerization reactor.

16. The method of claim 1 , wherein the specified value comprises a pressure loss in the range of about 5 pounds per square inch (psi) to 30 psi.

17. The method of claim 1 , wherein the determining of the friction factor comprises calculating the friction factor using a Colebrook equation.

18. The method of claim 1 , wherein the determining of the flow rate of the transfer slurry comprises determining the flow rate by mass balance of the polyethylene reactor system.

19. The method of claim 1 , wherein the transfer slurry has a higher average solids concentration than a first slurry present in the first polymerization reactor.

20. A method of operating a polyethylene reactor system, comprising:
polymerizing ethylene in a first polyethylene reactor to form a first polyethylene;
discharging continuously from the first polyethylene reactor a transfer slurry comprising diluent and the first polyethylene through a transfer line to a second polyethylene reactor;
polymerizing ethylene in the second polyethylene reactor to form a second polyethylene;
discharging continuously from the second polyethylene reactor a product slurry comprising diluent, the first polyethylene, and the second polyethylene;
determining, during the operation of the system, a velocity of the transfer slurry in the transfer line between the first polyethylene reactor and the second polyethylene reactor, wherein the velocity is determined by dividing a flow rate of the transfer slurry by a cross-sectional area of the transfer line; and
maintaining, during the operation of the system, the velocity greater than a specified value by adjusting a diluent flush to the transfer line to increase the velocity of the transfer slurry if the velocity drops to the specified value.

21. The method of claim 20 , wherein the specified value comprises a velocity in the range of about 95% to about 200% of a saltation velocity of the transfer slurry, and/or a velocity in the range of about 2 feet per second to about 10 feet per second.

22. The method of claim 20 , wherein the first polyethylene and the second polyethylene combine to give a monomodal polyethylene or a bimodal polyethylene.

23. A method of controlling a polyethylene reactor system, comprising:
polymerizing ethylene in a first polymerization reactor to form a first polyethylene;
discharging continuously from the first polymerization reactor a transfer slurry comprising diluent and the first polyethylene through a transfer line to a second polymerization reactor, polymerizing ethylene in the second polymerization reactor to form a second polyethylene;
discharging continuously from the second polymerization reactor a product slurry comprising diluent, the

Assignees

• Chevron Phillips Chemical Co Lp

Inventors

• Bhandarkar Maruti
• Benham Elizabeth Ann
• Gonzales Rebecca A
• Kufeld Scott E
• Mutchler Joel A
• Gill Catherine M
• Nguyen Thanh T
• Odi Timothy O

Classifications

• B01J19/1837 Primary

  Loop-type reactors · CPC title

• B01J2219/0006

  of the heat exchange medium · CPC title

• B01J19/2455

  provoking a loop type movement of the reactants (tubular loop-type reactors B01J19/2435; loop reactors having moving elements inside B01J19/1868) · CPC title

• B01J2219/00164

  controlling the flow · CPC title

• B01J2208/00088

  Flow rate measurement · CPC title