Patent GB-994807-A (GB)
Title: A method for the extraction of solvent from a solution and consequent concentration of the solution and apparatus therefor
Inventor: SAUNDERS MICHAEL JOSEPH
IPC: B01D9/00
Filed: 1962-06-28
Abstract: 994,807. Concentrating solutions by freezing. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 21, 1963 [June 28, 1962], No. 24927/62. Heading F4H. In a process for concentrating a solution by freezing out the solvent, a mixture of the solution and a volatile refrigerant is rotated in a tube 3 to form an outer annular layer of solution and an inner, annular layer of refrigerant, the pressure in the tube being such that the refrigerant evaporates and solvent crystals are formed at the interface between the layers. The tube 3 is rotated about its axis 25 and is disposed within a cylinder 4, a tubular guide member 7 being disposed within the annular space 5 between tube and cylinder to guide the slurry of refrigerant, solution and crystals from the tube 3 first rearwardly between tube and guide member then forwardly between guide member and cylinder and into a drum 8. The latter is integral with cylinder 4, is of gradually increasing diameter and contains a tubular filter 9 which is continuous with cylinder 4 and permits the passage of concentrated solution while retaining solvent crystals thereon. Gaseous refrigerant from tube 3 is forwarded through drum 8 by vanes 12. The concentrated solution passing through filter 9 is collected in an annular chamber 14 from which it is withdrawn and the refrigerant and crystals pass to a second drum 15 which is integral with drum 8 and has a portion of rapidly increasing diameter. Mounted in drum 15 for rotation therewith is a set of vanes 16 which directs refrigerant vapour to the periphery where the vapour, due to the increased radius of rotation, is compressed to an extent sufficient to condense the refrigerant on the crystals which are retained on a filter 19 mounted in the space 17 between drum 15 and the priphery of vanes 16 and are thus melted. The resultant liquid, liquid refrigerant and refrigerant vapour pass through filter 19 and separate under the influence of centrifugal force into distinct layers which are collected by respective annular ducts 21, 22 and 23. The vapour in duct 23 is further compressed due to the increased radius of rotation of the duet before being condensed externally of the assembly (see below). The above-described freezing, separating and melting assembly is shown at 38 in Fig. 4 which illustrates a process for concentrating sea-water with butane as the refrigerant. Sea-water is passed by a pump 31 through pre-coolers 33, 34 to a preliminary freezer 35 where a slurry containing 1% by weight of ice is formed by direct contact with butane from a reservoir 36. The slurry is then passed to the unit 38 to which liquid butane is supplied directly from reservoir 36. Butane from unit 38 passes through line 42 to a receiver 43 from which liquid butane is returned to unit 38 and butane vapour is supplied through line 44 to a compressor 45 which also receives butane vapour from the pre-freezer 35. The compressed butane is condensed at 47 by part of the sea-water from pump 31 and is returned to the receiver 43. Fresh water from unit 38 is withdrawn through line 40 and used as the coolant in pre-coolers 33, 34 while concentrated brine is withdrawn through line 41 via pre-cooler 33. The butane evaporates at 25‹ C. in tube 3 at a pressure of 13 p.s.i.a. and is compressed in drum 15 to a pressure of 15À5 p.s.i.a., the sea-water having its concentration raised from 3À5% to 6% by weight of solids in the process. In modifications, the tube 3 and filter 9 may be of gradually increasing diameter in the direction of fluid flow and in Fig. 3 (not shown) drum 8 is substantially greater in diameter than cylinder 4 and of relatively short axial length. " Freon " (Registered Trade Mark), n-butane, iso-butane, butene or propane may be employed as the refrigerant.