GB1247771A - Improvements in apparatus for the continuous crystallization of precipitation of at least one solute in solution in a solvent - Google Patents

Abstract

1,247,771. Apparatus for evaporation or cooling, film type; heat exchange crystallisation; centrifugal strainer. C.O.C.E.I. S.A. and F. LAURENTY. 11 Feb., 1969 [20 Feb., 1968; 8 Jan., 1969], No. 7426/69. Headings B1B, B1D and B1G. Crystals, suspended in solution, are increased in size by partial evaporation of solvent or by cooling the liquor in casing 20, the liquor being -fed through slots in pipes 25 so that it flows in film-form down the outer surfaces of a plurality of closed hollow elements 21 each comprising two thin heatconductive walls 22A, 22B which are disposed parallel at a short distance from each other and are sealed at the peripheral edges, the interior of the elements being supplied, in parallel, with heating or cooling fluid. In the case of evaporation the vapour evolved from the heated films flows through cone 27 to vessel 29 where the vapour is compressed by steam fed in through pipe 37; and the compressed vapour flows through nozzles 32 and 35 into the interior of elements 21, where the vapour condenses. The condensate is withdrawn from the lower portion of each element by a pipe 39 which is connected to a vacuum pump 31 (e.g. a liquid-ring pump). This pump is also connected to vessel 29. The liquor flows from the lower outer ends of elements 21 and through pipe 15 to vessel 13, where the liquor is circulated by a rotating wheel or helix driven by motor 14, so that the crystals are sorted according to size. Some of the thin liquor is returned to the evaporator body 20 through conduit 16, and the remainder is discharged, through pipe 33 and/or, pipe 34. Thick liquor, loaded with crystals, is pumped from vessel 13 through pipes 41, 42 into cyclone 43. The thick mass of crystals leaving cyclone 43 passes to a centrifuge 48 of the rotary sieve-basket type, where the largest crystals are separated and then discharged as product through outlet 53. The liquor which passes through the basket contains crystals of small size, and these are reduced to desired seed dimensions (e.g. 100Á) in ball grinding mill 65. The liquor is then introduced into vessel 13 through pipe 58. Fresh feed liquor is supplied to the apparatus through pipes 61 and 62. The heating elements may be provided with rollers which can be moved on rails. The thin walls of the elements may have a corrugated or zig-zag profile. A triple-effect evaporation is described wherein the vapours formed in the first effect are introduced into the heating elements of the second effect and the vapours formed in the second effect are introduced into the heating elements of the third effect, while the liquor flows over the heating elements in series in the reverse direction. The centrifuge, shown in Fig. 20, has a rotary basket 261 which is extended laterally by a plate 270 and is capped by a bell 271. The basket is attached to driving shaft 263. Associated with the basket are helical scraps 264 attached to shaft 266. The mass of crystals and liquor is introduced into the mouth 267 of the basket, and, the separated crystals, after sliding along the internal wall of the basket, are evacuated at 268. The dimensions of slot 276 is adjusted so that space 275 is full of liquid and any circulation of air through it is impossible.