1. Field of the Invention
The apparatus is a cylindrical tower with an inverted conical base; at the top of the column a deflector is placed to direct the incoming pellets onto the column so as to provide a surface with a toroidal contour; in the inverted conical base of the column a second deflector, in the form of two cones fastened together at their bases, is positioned on the central axis over the exit at the bottom apex of the cone so as to minimize or eliminate back-mixing of pellets as they flow through the base to the exit.
2. Prior Art
In polymerizations conducted in the presence of a solvent where solid polymer is produced, usually the resulting polymer, even after extrusion and/or cutting into pellets , retains some residual solvent, monomer and/or other residual volatiles which must be removed.
The removal of solvent or other residual volatiles from polymer pellets has been accomplished batchwise by passing hot gas and/or steam through a stationary bed of dry pellets, with or without agitation by tumbling, recirculation or stirring. However, it has previously not been possible to remove in a continuous process residual volatiles from particulate solids without contamination or mixing due to lack of control of pellet residence time during said removal. The relatively large volume of stripping medium and the low and variable residual solvent concentration in the pellets and vapor have heretofore made stripping and volatiles recovery inefficient and expensive.
Examples of the prior practice, which generally have been essentially batch operations employing either pellets having dry surfaces or suspensions of pellets in liquid, are found in Canadian Patent No. 836,977 of R. E. U. Routley, issued Mar. 16, 1970, U.S. Pat. No. 3,227,703 of P. S. Copenhaver, Jr. and R. L. Etter, Jr., issued Jan. 4, 1966, and U.S. Pat. No. 3,539,539 of J. Goetzke, issued Nov. 10, 1970. An apparatus designed as a bulking and mixing apparatus which shows some similarities to, but also critical differences from, the novel apparatus of the present invention is shown in British Patent Specification 846,198 of A. A. Karim, published Aug. 31, 1960. Apparatus for a solids flow system having an internal deflector is shown by U.S. Pat. No. 3,081,009 of F. D. Cooper issued Mar. 12, 1963. However, the function and location of the deflectors shown make them incapable of performing the function of the deflector of the apparatus of this invention of minimizing back-mixing in the reducing section.
The apparatus of this invention overcomes these problems. It also avoids the economic loss and air pollution caused by the venting to the atmosphere of residual volatiles, and it requires substantially less energy to operate, thus providing substantial savings in energy with resultant economy of operation.