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Techniques and systems for producing a polyolefin using reactors in series are described. Described embodiments include techniques and systems for polymerizing a monomer in a first polymerization reactor to form a first polyolefin, discharging a first slurry continuously from the first polymerizatio

Techniques and systems for producing a polyolefin using reactors in series are described. Described embodiments include techniques and systems for polymerizing a monomer in a first polymerization reactor to form a first polyolefin, discharging a first slurry continuously from the first polymerization reactor to a second polymerization reactor, and discharging a second slurry continuously from the second polymerization reactor. Using continuous take-off devices disposed on either or both reactors, pressure control may be attained such that the rate of transfer between and withdrawal from both reactors are within a desired range.

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1. A method of producing a polyolefin, comprising: providing a feed comprising a diluent and a first monomer to a first polymerization reactor;polymerizing the first monomer in the first polymerization reactor to form a first polyolefin in a first slurry;discharging a transfer slurry comprising the

1. A method of producing a polyolefin, comprising: providing a feed comprising a diluent and a first monomer to a first polymerization reactor;polymerizing the first monomer in the first polymerization reactor to form a first polyolefin in a first slurry;discharging a transfer slurry comprising the first polyolefin and the diluent continuously from the first polymerization reactor to a second polymerization reactor;polymerizing a second monomer in the second polymerization reactor to form a second polyolefin in a second slurry;discharging the second slurry from the second polymerization reactor; andcontrolling a pressure in the first polymerization reactor and a pressure in the second polymerization reactor by modulating only continuous take-off of the second slurry from the second polymerization reactor along with the feed into the first polymerization reactor. 2. The method of claim 1, wherein the first polyolefin is polyethylene. 3. The method of claim 2, wherein the first polymerization reactor and the second polymerization reactor are similarly sized. 4. The method of claim 1, wherein the first polymerization reactor and the transfer line are substantially free of gravity settling. 5. The method of claim 1, wherein the transfer slurry has a higher average solids concentration than the first slurry. 6. The method of claim 1, wherein the first polymerization reactor is operated under a first set of conditions to produce the first polyolefin having a first molecular weight distribution and the second polymerization reactor is operated under a second set of conditions to produce the second polyolefin having a second molecular weight distribution, and the first and second molecular weight distributions are different. 7. The method of claim 1, wherein the diluent comprises isobutane. 8. The method of claim 1, wherein the diluent comprises propane. 9. The method of claim 8, wherein the first reactor, the second reactor, or a combination of both is operated at least at a critical temperature and/or at least at a critical pressure of fluid reactor contents, the fluid reactor contents comprising all reactor contents. 10. A system for producing a polyolefin, comprising: a first polymerization reactor;a second polymerization reactor disposed downstream of the first polymerization reactor;a conduit fluidly connecting the first polymerization reactor and the second polymerization reactor in series; anda continuous take-off device disposed on a downstream segment of the second polymerization reactor and configured to control a flow of a transfer slurry from the first polymerization reactor, through the conduit, and to the second polymerization reactor;wherein the ratio of an equivalent length of the conduit to a longest equivalent length of the first polymerization reactor and the second polymerization reactor is 25% to 50%. 11. The system of claim 10, comprising a ram valve with an extension configured such that it is oriented into a downstream flow of a stratified slurry circulating within the first polymerization reactor, wherein the ram valve is angled in a direction towards the downstream flow. 12. The system of claim 10, wherein the continuous take off device is configured to facilitate a flow of the transfer slurry through the conduit using a motive force generated at least partially by a continuous feed of diluent and monomer into the first polymerization reactor.