Patent GB-1118413-A (GB)
Title: Freeze purification method and apparatus
IPC: C02F1/22
Filed: 1965-12-13
Abstract: 1,118,413. Concentrating solutions by freezing. WORTHINGTON CORP. 13 Dec., 1965 [15 Jan., 1965], No. 52936/65. Heading F4H. In a process for fractionating solutions by freezing the solution is flash-cooled to form solvent crystals on a crystal-forming surface, and the crystals are melted while on such surface. As shown, sea-water from line 16 is deaerated at 18 and forwarded by pump 30 through heat exchanger 32 to spray nozzles 38 disposed above ice-forming surfaces 40 in a low-pressure chamber 12. The solution flashevaporates to form ice on surfaces 40 and the vapour evolved is condensed on refrigerant tubing 44 over which an anti-freeze sodium chloride solution is continuously circulated by pump 52 and nozzles 50. The solution supply to nozzles 38 is then terminated, a valve 56 is opened and a saline solution of relatively low concentration is supplied by a pump 58 from a reservoir 60 to nozzles 38 to wash the ice on surfaces 40. Initially, such washing produces saline solution of relatively high concentration which is withdrawn from the bottom of chamber 12 via line 62, valve 64, pump 63 and heat exchanger 32. Valve 64 is then closed and washing continued with the now less concentrated solution from chamber 12 being returned to reservoir 60 via a valve 68. After washing, the ice is melted by supplying relatively hot refrigerant to tubing 44 to evaporate the water previously condensed thereon from the sodium chloride solution. The resultant steam condenses on and melts the ice on surfaces 40, the fresh water being withdrawn by pump 74 via line 62 and valve 72 and forwarded as product through heat exchanger 32. The above sequence is also carried out in a second low-pressure chamber 14 which is identical, and operates out of phase, with chamber 12, i.e. the coils 44 and 44<SP>1</SP> of the respective chambers form part of a reversible heat pump system having a compressor unit 70. Part of the hot compressed gas from the latter is used to concentrate part of the sodium chloride solution circulated over tubes 44 or 44<SP>1</SP>, the water vapour evolved during such concentration being condensed on the evaporator of a supplementary compression refrigeration system 66 and added to the product. This part of the system is illustrated in detail in Fig. 4 (not shown) while in Fig. 5 (not shown) the concentration is effected by part of the discharge of the compressor of refrigeration system 66. The above system may operate without the anti-freeze sodium chloride solution, in which case ice is alternately formed and melted on tubes 44 and 44<SP>1</SP>. In a modification (Fig. 2, not shown) two working compartments (86, 88 and 90, 92) are provided in each of the low-pressure chambers, flaps (146, 148, 150, 152) are provided for controlling communication between the compartments and the heating/cooling coils (142, 144) in the respective chambers and lithium bromide solution is circulated over the coils at relatively high temperature to absorb water vapour evolved in the freezing step. The freezing, initial washing, final washing and melting steps are carried out at different times in the four compartments and coils (142, 144) are supplied with either cool water from a source (154) for the absorption step or steam from a source (155) for the regeneration of water vapour. Part of the circulating lithium bromide solution is reconcentrated either in the system of Fig. 5 in the manner indicated above or in the system of Fig. 6 (not shown) in which the lithium bromide is sprayed over tubes (384) supplied with steam, hot water or other heating medium and the evolved water vapour is condensed on tubes 386, supplied with sea-water, and added to the product. In a further embodiment (Fig. 3, not shown), the washing step is eliminated, four seriallyconnected freezing/melting vessels (300, 302, 304, 306) being provided. The melt from one vessel is supplied to the next in the series to produce a melt of the desired purity in vessel (306).