Patent GB-993263-A (GB)
Title: Process for removing solute from solutions
IPC: C02F1/22
Filed: 1962-03-13
Abstract: 993,263. Concentrating solutions by freezing. NORTH AMERICAN AVIATION Inc. March 13, 1962 [March 23, 1961], No. 9654/62. Heading F4H. In a solution purification process in which a solution of intermediate concentration is contacted with a vaporizable liquid refrigerant to form solids, i.e. ice or a refrigerant hydrate, and a more concentrated solution, the solids being melted or decomposed by contact with warm refrigerant vapour to form a less concentrated solution, one or both of the resultant solutions is or are freed of refrigerant by a liquid absorbent drawing a high solubility for the refrigerant which is subsequently recovered from the absorbent. As shown, sea-water from a source 10 is pre-cooled at 12 to near its freezing point by direct contact with kerosene which enters and leaves the precooler through lines 14 and 17 respectively. The sea-water then passes through line 15 to a freezer 40 where it is contacted with cold liquid butane from line 53, the resultant ice-brine slurry being passed through line 61 to a washer 60 which utilizes unprocessed sea-water from a line 62. Ice leaving the washer through line 64 is melted in a vessel 39 by warm refrigerant vapour from the outlet line 82 of a primary compressor 42, vapour from the freezer 40 and melter 39 being supplied to the compressor inlet through lines 56 and 41. Brine from the freezer and water from the melter pass through lines 59 and 58 to vessels 38 and 37 in which they are contacted with kerosene to remove refrigerant therefrom. Product water and brine leave the vessels through lines 77 and 66 while kerosene containing absorbed butane is supplied through lines 83 and 84 to line 14 for use in the pre-cooler 12. Part of the warm kerosene in line 17 is passed through line 77 to an absorber 18 in which it absorbs a butane vapour stream entering through line 19, dissolved air and inert gases being vented through line 21 and vent 22 and the kerosene/butane stream being passed through line 23 and cooler 24 to a surge tank 20 from which remaining gases are vented through line 27 and vent 22. The remaining kerosene from line 17 is also passed to the tank 20 whence it is pumped through line 28, part of the kerosene from line 28 being passed through lines 35, 36, 75 and 79 to the vessels 37 and 38, and part through line 29, heat exchanger 30 and line 31 to a steam still 32 where butane vapour is distilled off through line 34. Hot kerosene from the still passes through line 33, heat exchanger 30, line 67 and a vessel 65, in which it contacts brine from line 66, and is finally returned to the vessel 38 through lines 69 and 79. The butane vapour in line 34 is partly refluxed through line 76, condenser 74 and line 78 and partly supplied to a secondary compressor 43 which discharges via line 44 into two lines 45 and 46. The latter leads to a condenser 47 from which liquid butane passes to a flash cooler 72. Butane vapour from the latter is passed through line 81 to compressor 43 and cooled liquid refrigerant is supplied through line 53 to freezer 40. Butane vapour from line 45 passes to a condenser 48, a separator 50, from which any remaining vapour is passed to line 46 through line 52, and line 51 to the still 32 where the refrigerant is freed of dissolved kerosene. The liquid butane leaving the melter 39 through line 54 is passed to a flash cooler 55 from which the liquid component is passed to flash cooler 72 and the vapour component to the absorber 18 through line 19. Additional steps which may be included in the process are those of washing the ice from washer 60 with purified water, adding make-up butane to flash cooler 72 and adding kerosene to line 67. In a modification (Fig. 3, not shown) isobutane is used as the refrigerant and also as the medium employed to precool the sea-water. The isobutane is also heat exchanged with the product water and waste brine in separate vessels from which the water and brine pass to absorbers to be contacted with octane flowing in a closed circuit which includes the steam still. An isobutane vapour stream is passed to one of the absorber vessels, which is vented to remove air and inert gases, and the isobutane vapour from the steam still is returned to the refrigerant cycle. The sea-water is partially deaerated before precooling and provision may be made for adding make-up octane and isobutane to the absorber and refrigerant cycles.