Patent GB-1198141-A (GB)
Title: A Method of, and Apparatus for, Fractionating Slurries and Classifying Granular Material by Size
Inventor: NICOL WILSON MENZIES
IPC: C13B30/06
Filed: 1967-01-10
Abstract: 1,198,141. Crystallizing sucrose. TATE & LYLE Ltd. Dec. 4, 1967 [Jan. 10, 1967], No. 1320/67. Heading C6B. [Also in Division B2] A slurry of granular material, e.g. a masseculte containing sugar crystals, is separated into at least two fractions by introducing the slurry into a vessel rotating about a substantially vertical axis so that the slurry in the vessel assumes a substantially paraboloidal surface and flows upwardly adjacent to the wall of the vessel, and separating the upwardly flowing slurry into at least two fractions disposed at different distances from the axis of rotation of the vessel. In an apparatus, Fig. 1, comprising a rotating vessel 1 within which a hollow cylindrical baffle 4 is secured by means of arms 5, a liquid is continuously fed in to the vessel by means of a pipe 8 so that it assumes a paraboloidal surface 9 and spills out partly over the upper edge 2 of the vessel and partly over the upper edge 7 of the baffle. The slurry of granular material is fed on to the surface 9 by means of a pipe 10 and the granular material in the resultant slurry travels outwardly and upwardly, the resultant slurry being separated into two fractions by means of the baffle 4, slurry containing relatively large and relatively small particles of granular material being discharged over the edges 2 and 7 respectively, so that the granular material is at the same time classified into two size fractions. The liquid first introduced in the vessel and the liquid of the original slurry may have the same or different chemical properties and their physical properties, e. g. density and viscosity may differ. A number of radially spaced coaxial baffles may be used to obtain more than two fractions. In Fig.2, the vessel 1 is driven by an electric motor 13 through gearing 14. Massecuite from a crystallizing boiling pan 21 is fed by a pump 23 and a pipe 10 on to a stationary annular plate 19 from which it flows on to the surface 9 of liquid supplied through the pipe 8. Massecuite containing small sugar crystals discharges over the edge 7 of the baffle into an annular vessel 18 and is returned to the pan 21 via a pipe 24. The larger crystals are deflected into the annular space 12 and discharge with massecuite over the upper edge of the vessel 1 into an annular vessel 16, the massecuite and crystals flowing via a pipe 25 into a vessel 16. The liquid fed to the vessel 1 by the pipe 8 may be massecuite which may be that in the vessel 26 containing the larger crystals. The apparatus may be used as a crystal transfer regulator between a series of boiling pans with crystals of different sizes. In a modification of the Fig. apparatus, Fig. 3 (not shown) there is no separate layer of liquid formed in the vessel and the diluted slurry is fed through an axially disposed pipe directly on to the bottom of the vessel and is separated into two fractions of different solids concentration. Alternatively, the fraction passing inwardly of the baffle may be substantially free of solids. Instead of having an axially disposed slurry feed pipe, the vessel, Fig.4 (not shown), may have a central hole in its base through which the slurry flows when the vessel, in operation, is immersed in a body of diluted slurry. In a sugar crystallization plant, Fig. 5, the vessel 211 is partially immersed in a slurry of sugar crystals in massecuite contained in a crystallizer 221. Slurry passes through a hole 207 into the vessel 211 where it is separated into a concentrated and a dilute fraction. The concentrated fraction discharging over the edge of the vessel is recycled to the body of slurry in the crystallizer and the dilute fraction substantially free of sugar crystals passes over the edge of the baffle 204 and along a line 228 to an evaporator 226 and is recycled after concentration (without crystal formation) therein to the crystallizer via a line 230. The crystallizer is operated continuously, fresh crystal-freed sugar solution being continuously supplied to the evaporator 226 via a line 230. Massecuite from the crystallizer is fed a long a line 210 to a fractionating vessel such as that of Fig. 2 and classified, the massecuite with small particle size being recycled to the crystallizer via a line 224. The plant may be modified by replacing the fractionating vessel by that of Fig. 3 (not shown) located outside the crystallizer and connected thereto by pipes.