High-pressure polymerization system and high-pressure polymerization process for the polymerization of ethylenically unsaturated monomers

A high-pressure polymerization system comprising

• a) a continuously operable polymerization reactor having a reactor inlet and having a reactor outlet and
• b) a reactor blow down system adapted and arranged to be in fluid communication with the polymerization reactor, the reactor blow down system comprising
• b1) a reactor blow down vessel, having a circular design over a major portion P having a length L, a diameter D and a L/D-ratio in the range from 1.75 to 10.0, and containing an aqueous quenching medium,
• b2) a release line, connecting the polymerization reactor with the reactor blow down vessel and having a release line outlet for expanding a content of the high-pressure polymerization system comprising polymer and gaseous components into the reactor blow down vessel, wherein the release line outlet is located above a maximum level for the aqueous quenching medium, and
• b3) a first emergency valve arranged in the release line and adapted to open and close fluid communication between the polymerization reactor and the reactor blow down system,
• wherein the release line outlet has a joining piece, having a central axis and arranged such that an angle (α), formed between the central axis of the joining piece and a tangent located at the intersection of the central axis with the circular periphery of the major portion P of the reactor blow down vessel and having the same inclination as the central axis with respect to the horizontal plane containing this intersection, is in the range from 5° to 70°, and
• wherein the reactor blow down vessel further comprises a vent stack containing a constricted section.