Vacuum freezing multiple phase transformation process and apparatus for use therein

摘要

Improved apparatuses and methods of operation for conducting the separation process entitled "Vacuum Freezing Multiple Phase Transformation Process (denoted as VFMPT Process)" have been introduced. Processing zones and valving means are properly arranged so that operations in most processing zones are continuous. An improved VFMPT plant can be operated simply and reliably and be constructed at a low cost. Corrosion problems, use of a low pressure compressor, use of an absorbing solution have been eliminated. A feed containing a volatile solvent and one or more non-volatile solutes is separated to produce a purified solvent product and a concentrate by the following steps: (a) a feed is flash vaporized in a vacuum freezing zone to form a first vapor and a first condensed mass containing solvent crystals and mother liquor, the pressure of the first vapor being lower than the triple point pressure of the solvent; (b) the first condensed mass is separated into a mass of purified solvent crystals and a concentrate in a crystal washing unit; (c) the first vapor is brought to a liquid state in a vapor liquefaction zone comprising several sub-zones by a two stage transformation involving vapor desublimation and desublimate melting operations; (d) a solvent stream is continuously vaporized in a thin film evaporator within a vapor generation zone to produce a continuous stream of second vapor whose pressure is somewhat higher than the triple point pressure of the solvent, (e) the solvent vapor is brought in contact with the purified solvent crystals to thereby melt the crystals and condense the vapor. The desublimate melting operation may also be accomplished by bringing a part of the second vapor in contact with the desublimate. A unique set of valving means are used to control flows of first and second vapors to the vapor liquefaction sub-zones.