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United States Patent 4117548
Douris , ê et al. September 26, 1978

Screw vent

Craig September 26, 1978

Abstract

A vent for a devolatilizer includes a means defining a vent opening in the cage of the devolatilizer and a vent duct which communicates with the vent opening. Gas escapes into a cylindrical vent chamber in the vent duct. The chamber is cleaned by a vent screw which is rotated in the chamber and which includes a screw body of minimal diameter and a helical screw flight portion of a pitch which is sufficiently large such that the velocity of the vapor leaving the cage through the vent duct is maintained below a predetermined maximum vapor velocity. This maximum vapor velocity is set such that the amount of fine material which is entrained in the escaping vapor is minimized. A vapor return duct is connected to the vent chamber for extracting vapor from the chamber so that it may be recycled or disposed of. In one embodiment, the pitch of the vent screw flights is reduced in the upper portion of the vent chamber to accelerate the vapor and keep entrained in the gas any fines which may have escaped from the devolatilizer.