GB1024447A - Process for separation of solvent from solute by freezing of solvent - Google Patents

Abstract

1,024,447. Concentrating solutions by freezing; refrigerating. S. UMANO. Nov. 20, 1962, No. 43854/62. Heading F4H. In a process for freezing out solvent from a solution by direct contact with a vaporizing liquid refrigerant, the solution and refrigerant are agitated during freezing to maintain at least a portion of the refrigerant dispersed below the surface of the solution. As shown in Fig. 9, liquid butane is introduced into the bottom of a freezing vessel containing sea water and after rising through the latter to form a layer h on the surface is dispersed through the solution in the form of discrete droplets o by horizontal rotary agitators b. The amount of refrigerant supplied is such that it is entirely dispersed when the agitators are operating at their maximum speed. The droplets cool the solution, while evaporating, to form the crystals p and it is stated that the droplets are dispersed to such a depth in the solution that the hydrostatic head thereon does not fall without the range 10 to 100 mm. of mercury. The ice crystals are retained in the freezing vessel until they reach a predetermined size (e.g. 3 to 7 mm.) and then flow over a weir at one end of the vessel (Fig. 8, not shown), to collect in a non-agitated zone from which a slurry of ice and concentrated brine is withdrawn. In the process shown in Fig. 4, sea-water, pre. cooled by gasoline in a direct contact heatexchanger d 1 , is supplied by pump k to the freezing vessel a which is supplied with refrigerant from a main condenser b. Refrigerant vapour is withdrawn from vessel a by a compressor g and forwarded to condenser b while ice-brine slurry is withdrawn from vessel a by a pump i and forwarded to an ice-separator c. The separated ice is slurried with fresh water and supplied by pump j to condenser b where it is melted in condensing part of the refrigerant vapour, the uncondensed vapour being withdrawn by an auxiliary compressor h, liquefied in auxiliary condenser e, flashcooled in vessel f and supplied to vessel a. Fresh water from condenser b is in part used to slurry ice in separator c and the remainder is passed to a direct contact heat-exchanger d 3 to cool the gasoline used in heat-exchanger d 1 and is then discharged through line o. Concentrated brine from separator c is returned to vessel a from which it is discharged through line p via a direct contact heat-exchanger d 2 which is in parallel with heat-exchanger d 3 in the gasoline circuit. In the modification of Fig. 5 (not shown), heat-exchangers d 1 , d 2 and d 3 are omitted and the concentrated brine and fresh water discharge streams used to cool an auxiliary condenser, an externally-cooled auxiliary condenser also being provided. In a further modification (Fig. 6, not shown), three freezer vessels a 1 , a 2 , a 3 and three separators b 1 , b 2 , b 3 are provided. Incoming sea-water from line j is used to slurry ice crystals in separator b 2 and the slurry is passed through line i 2-1 to freezer a 1 , from which ice brine slurry passes through line f 1 to separator b 1 . The ice separates in the latter is slurried with fresh water from the main condenser (not shown) and discharged at e, part of the filtrate is returned to a 1 , through line g, and the remaining filtrate is passed through line i 1-3 to slurry icecrystals in separator b 3 . This slurry passes through line i 3-2 to freezer a 2 from which icebrine slurry passes through line f 2 to separator b 2 . Part of the filtrate from the latter returns to a 2 through line g 2 and the remainder passes to freezer a 3 from which ice-brine slurry passes to separator b 3 . Part of the filtrate from the latter returns to a 3 through line g 3 and the remainder is discharged from the system through line k. Refrigerant is supplied to the freezers through line n and withdrawn therefrom by compressors c 1 , c 2 and c 3 . In a still further modification (Fig. 7, not shown), the process utilizes an absorption refrigeration system having an absorber b in which the absorbent is cooled by the icewater slurry from separator c, generator d, condenser e and heat-exchangers f and g. An auxiliary absorber may be provided and a plurality of freezers operating in series or in parallel can be used.