This disclosure relates to fluid separation systems and methods. More particularly, this invention relates to systems and methods for separating polymer particles from reaction mixtures in polymerization processes.
Polymerization reactors convert relatively low cost olefin monomers (e.g., ethylene, optionally in combination with one or more comonomers) into valuable polyolefin product (e.g., polyethylene).
The reactors are generally operated at relatively high pressure (e.g., 200 to 310 MPa) and relatively high temperature (e.g., 150 to 450° C.). The reaction is highly exothermic. If the reaction mixture overheats, the olefins will decompose into carbon, hydrogen, and methane. Moreover, excessive temperature and/or pressure can present safety concerns. For these reasons, it is important to conduct the polymerization in a controlled manner and, if necessary, implement emergency shut-down of the reactor.
Emergency shut-down generally requires relieving the temperature and pressure conditions within the reactor by venting the reactor contents (e.g., a mixture of unreacted components and polymer particles) into the atmosphere.
It would be desirable to have a system and method that reduces, or effectively eliminates, the emission of polymer particles into the atmosphere during reactor shut-down.
In one aspect, this disclosure relates to systems for separating particles from a fluid. The system comprises: (i) a vessel having a fluid inlet and a fluid outlet; and (2) a baffle assembly located within the vessel. The baffle assembly has a plurality of baffles that can provide a change in direction to fluid entering the vessel.
In another aspect, this disclosure relates to methods for separating particles (e.g., polymer) from a reaction mixture during shut-down of a polymerization reactor. The method comprises: (i) opening a valve in the polymerization reactor; and (ii) discharging at least a portion of the reaction mixture into a separation system. The separation system may comprise a vessel having a fluid inlet and a fluid outlet and a baffle assembly concentrically positioned within the vessel. The baffle assembly may comprise a plurality of baffles that form an annular ring. The plurality of baffles may be axially extending. Each of the plurality of baffles may be oriented in the same direction as fluid entering the vessel.
In one embodiment, the fluid inlet can introduce fluid substantially tangentially to the wall of the vessel.
In one embodiment, the fluid comprises a polymer, such as polyethylene, suspended therein.
These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description and appended claims.
Various specific embodiments, versions and examples of the invention will now be described, including preferred embodiments and definitions that are adopted herein for purposes of understanding the claimed invention. While the following detailed description gives specific preferred embodiments, those skilled in the art will appreciate that these embodiments are exemplary only, and that the invention can be practiced in other ways. For purposes of determining infringement, the scope of the invention will refer to any one or more of the appended claims, including their equivalents, and elements or limitations that are equivalent to those that are recited. Any reference to the “invention” may refer to one or more, but not necessarily all, of the inventions defined by the claims.
That said, described herein are systems and methods for separating particles (e.g., solid polymer) from fluids, particularly during shut-down of polymerization reactors. Exemplary separation systems comprise: 1) a vessel having a fluid inlet and a fluid outlet; and (2) a baffle assembly.
The vessel may be any structure sufficient to contain fluid within.
The vessel further comprises a fluid inlet sufficient to deliver fluid into the vessel. In accordance with various exemplary embodiments, the fluid inlet introduces the fluid into the vessel at a desired trajectory. For example, the fluid inlet may introduce fluid toward, or substantially tangentially to, the wall of the vessel.
In various exemplary embodiments, the fluid inlet is located in the bottom half of the vessel. For example, a vessel having a height Hv may have a fluid inlet located at a height of about 0.1Hv to about 0.7Hv, or about 0.4Hv, from the bottom of the vessel.
The vessel further comprises a fluid outlet sufficient to discharge fluid.
In accordance with various exemplary embodiments, the diameters of the fluid inlet and fluid outlet may be sized to control the speed of entry and/or exit of the fluid. For example, the diameter of the fluid inlet may be relative small (e.g., about 0.04 to about 0.3 m) to introduce fluid into the vessel at a relatively high speed and/or the diameter of the fluid outlet may be relatively large (e.g., about 0.5 to about 1.5 m) to discharge fluid at a relatively low speed.
The fluid may be any composition containing particles, whether in solid, gas, or aqueous form. For example, the fluid may comprise any known or hereinafter devised polymerization reaction components in the gas phase (e.g., one or more of olefin monomers such as ethylene-derived units or propylene- derived units, comonomers such as a-olefins, solvents, initiators, catalysts, additives, hydrogen, and/or the like) in combination with one or more particles (e.g., polymers such as those containing ethylene-derived units or propylene-derived units) suspended therein (e.g., a polyolefin, such as polyethylene or polypropylene).
The separation system further comprises a baffle assembly. The baffle assembly may be any device, structure or system that provides a change in direction to fluid entering the vessel. The change in direction: (1) acts as a separating mechanism to remove polymer and other particles from the fluid; and/or (2) lengthens the resident time of the fluid within the vessel, thereby allowing more time for polymer to deposit onto a surface within the vessel. In various embodiments, the baffle assembly further provides a guided flow path for fluid within the vessel.
In an exemplary embodiment, the baffle assembly comprises a plurality of baffles. By way of example,
In various embodiments, the plurality of baffles is non-motorized, i.e., operable to rotate but not rotated under motor power.
In various embodiments, the baffle assembly extends at least a distance of about 0.6Hv to about 0.9Hv from the top of the vessel, for a vessel of height Hv. The conduit (ID of the baffle assembly) may have a diameter Dc of about 0.15Dv to about 0.6Dv, for a vessel having a diameter Dv.
In accordance with various exemplary embodiments, each of the plurality of baffles is oriented in the same direction as fluid entering the vessel via the fluid inlet. As used herein, the phrase “in the same direction as fluid entering the vessel” means at an angle between 0 and 90 degrees relative to the direction of entry of the fluid entering the vessel. For example,
In one embodiment, each of the plurality of baffles is substantially rectangular. Moreover, each of the plurality of baffles may have a length of about 0.6Hv to about 0.9Hv m and/or a width of about 0.1 to about 0.5 m. In one embodiment, each of the plurality of baffles is curved along its width to facilitate deflection of the fluid. For example,
As shown in
In various embodiments, the baffle assembly comprises one or more baffle supports. The baffle support may be any device, structure or system that provides additional stabilization along the length of the baffle assembly.
In various exemplary embodiments, the baffle assembly is integrally formed with the vessel. In other embodiments, the baffle assembly is a separately-formed insert that may be retrofitted to an existing vessel or separation system. The insert may be attached to the vessel using any known or hereinafter devised system or method. For example, as illustrated in
In various embodiments, and as shown in
In various embodiments, the separation system further comprises a barrier to prevent fluid from prematurely exiting the system.
In various exemplary embodiments, the separation system further comprises a liquid reservoir within the vessel. For example, as shown in
In various embodiments, the reservoir liquid may be drained from the vessel and/or may undergo further processing to remove the particles. The reservoir may be recharged.
In various embodiments, one or more separation systems may be employed in parallel or in series to further control and reduce the amount of polymer released into the atmosphere.
In operation, and with reference to
In various embodiments, the invention relates to a process for shutting down a polymerization system (e.g., emergency shut down due to excess pressure and/or temperature). With reference to
In operation, and with continued reference to
In the event the reactor needs to be shut down (e.g., it exceeds a predetermined pressure or temperature), feed stream 578 is stopped and the pressure within reactor 588 is let down by opening one or more valves 589, which transfers reaction mixture 591 comprising a mixture of gas and polymer particles to separation system 501. As used herein, “opening one or more valves” includes manual opening as well as automatic actuation and the like. Upon entry into separation system 501, the fluid mixture contacts the baffle assembly which separates the polymer before releasing gas 598 into the atmosphere. Residual polymer 599 can then be removed from separation system 501.
The advantages of the compositions described herein will now be further illustrated with reference to the following non-limiting Example 1.
Polyethylene is manufactured in a tubular reactor (vol. 500 L) at a pressure of about 300 MPa and a temperature of 310° C. The reactor is equipped with valve that opens when reactor shut-down is needed (e.g., predetermined reactor conditions, such as pressure or temperature limits, are exceeded). Upon activation of the valve, the reactor contents are released into a separation system (vol. 8000 L). The fluid inlet is oriented tangentially to the wall of the vessel of the separation system. The baffle assembly (e.g., annular ring) are axially extending such that the inner diameter of the annular ring forms a conduit with the fluid outlet. The individual baffles of the baffle assembly curved along their width from the inner diameter of the baffle assembly to the outer diameter of the baffle assembly in the same direction as fluid entering the vessel. It is expected that for 100 kg of polymer in the reactor, 80 kg of polymer will be collected in the separation system and 20 kg of polymer will be discharged into the atmosphere (polymer retention of 80%).
The embodiments and examples set forth herein are presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and use the invention. However, those skilled in the art will recognize that the foregoing description have been presented for the purpose of illustration and example only. The description set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the claims.
This application relates to PCT Application No. PCT/US2008/087501 entitled “High Pressure Polymerization Process,” filed on Dec. 18, 2008, and PCT Application No. PCT/US2009/050491 entitled “High Pressure Radical Polymerization Process,” filed on Jul. 14, 2009. These applications are incorporated by reference herein in their entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US09/64429 | 11/13/2009 | WO | 00 | 6/6/2012 |