Separation Vessels For Use In Polymerization Processes And Methods For Cleaning Same

Abstract

Both a system and method for cleaning a low pressure separation vessel of a high pressure polyethylene polymerization plant are provided. The system includes a polytetrafluoroethylene lining that covers the interior surfaces of the vessel, and a cover mounting assembly including an annular clamp for detachably mounting a cover over the vessel. The mounting assembly includes a clamp actuator for quickly securing and releasing the cover with respect to a top rim of the vessel. The vessel is drained of liquid polyethylene and allowed to cool to ambient temperature, thus creating a frozen “skin” of polyethylene around the interior surfaces of the vessel. The clamp actuator releases the cover. The polyethylene skin is peeled off the interior sides the vessel and gathered up at the top to form a neck, thus peeling the polyethylene skin away from the polytetrafluoroethylene lining along with any degraded polymers or other impurities that have accumulated on the interior surfaces of the vessel.

1 - 29 . (canceled) 
     
     
         30 . A separation vessel for use in a polymerization process comprising:
 a detachable cover; and   a lining that covers at least a portion of the interior surfaces of the vessel, wherein such lining comprises a layer which is low-stick with respect to a polymer resulting from the polymerization process.   
     
     
         31 . The system defined in  claim 30 , wherein the polymer comprises at least one of polyethylene and polypropylene. 
     
     
         32 . The system defined in  claim 30 , wherein the vessel is a component of a high pressure polymerization plant. 
     
     
         33 . The system defined in  claim 30 , wherein the cover has a mounting assembly adapted to maintain the cover in a pressure-tight relationship with the vessel. 
     
     
         34 . The system defined in  claim 33 , wherein the mounting assembly comprises a clamp. 
     
     
         35 . The system defined in  claim 30 , wherein said low-stick layer comprises polytetrafluoroethylene. 
     
     
         36 . The system defined in  claim 35 , wherein said low-stick layer has a dry film thickness between about 0.02 and 0.20 mm. 
     
     
         37 . The system defined in  claim 30 , further comprising a layer of metal applied over the interior surfaces of the vessel to promote adhesion between the low-stick lining and the interior surfaces of the vessel. 
     
     
         38 . The system defined in  claim 37 , wherein said layer of metal is a layer of nickel between about 0.050 and 0.150 mm thick. 
     
     
         39 . The system defined in  claim 30 , wherein at least a portion of the interior surface of the cover comprises the low-stick lining. 
     
     
         40 . The system defined in  claim 39 , wherein the dry film thickness of the low-stick lining on the interior surface of the cover is between about 0.04 and 0.15 mm. 
     
     
         41 . The system defined in  claim 33 , wherein the mounting assembly comprises a clamp actuator that secures and releases the clamp into and out of a clamping position that pulls together said cover and a top rim of said vessel. 
     
     
         42 . The system defined in  claim 41 , wherein the mounting assembly further includes a gasket interposed between the cover and the top rim of the vessel. 
     
     
         43 . The system defined in  claim 41 , wherein the mounting assembly further includes opposing flanges disposed along an outer periphery of both the cover and a top rim of the vessel, wherein the clamp captures and pulls together said opposing flanges when in said clamping position. 
     
     
         44 . The system defined in  claim 30 , further comprising a hoist that pulls away a polymer skin present on the low-stick lining that covers the interior surfaces of the vessel. 
     
     
         45 . The system defined in  claim 41 , wherein the mounting assembly comprises a mounting mechanism including an annular clamp for detachably mounting said cover over the top rim of the vessel. 
     
     
         46 . The system defined in  claim 44 , further comprising at least one scraping tool for separating the polyethylene skin present on the polytetrafluoroethylene lining that covers the interior surfaces of the vessel. 
     
     
         47 . The system defined in  claim 45 , wherein the clamp comprises an actuator having at least one hydraulic cylinder for securing and releasing the clamp into and out of a clamping position that pulls together said cover and the top rim of the vessel. 
     
     
         48 . A method for cleaning a separation vessel containing a polymer comprising:
 providing a separation vessel having a detachable cover and a low-stick lining with respect to said polymer that covers at least a portion of the interior surfaces of the vessel;   removing said cover;   emptying the vessel of liquid polymer;   cooling the vessel to form a skin of said polymer on said low-stick lining; and   removing the polymer skin present on the lining.   
     
     
         49 . A method for removing polymer from a separation vessel in a polymerization system comprising:
 providing a separation vessel having a removable cover and a low-stick lining with respect to said polymer that covers at least a portion of the interior surfaces of the vessel;   removing said cover;   stopping the flow of polymer to the separation vessel;   emptying the vessel of substantially all of the liquid polymer;   cooling the vessel to form a skin of said polymer on said low-stick lining; and   unpeeling the polymer skin present on the lining.