Improvements in or relating to a method for producing purified water from aqueous saline solutions

1,074,144. Purifying saline solutions; refrigerating. BRITISH PETROLEUM CO. Ltd. May 25, 1965 [April 28, 1964], No. 17539/64. Heading F4H. In a method of obtaining purified water from an aqueous saline solution by contacting the solution with a paraffin having 1 to 4 carbon atoms per molecule to from a hydrate, the hydrate is washed first with incoming untreated solution, which is thus pre-cooled, then with part of the purified water. As shown, sea-water from line 15 passes through a first washing stage 12 and line 18 to a vessel 10 where it is contacted with propane introduced through line 21 and expansion valve 30 to form propane hydrate which is removed through line 19. The concentrated brine passes through line 16 to a second vessel 11 and is contacted with propane from line 22 and expansion valve 31, propane hydrate being removed through line 20 and concentrated brine through line 17. The hydrates are combined and passed through first and second washing stages 12 and 13 to a hydrate-decomposing stage 14 for direct contact with compressed propane vapour from compressors 50 and 51. From stage 14, liquid refrigerant is returned to vessels 10 and 11 and purified water is discharged through line 29, part of the water being passed through line 25 to the second washing stage and, after use, being forwarded through line 26 to line 15. Additional cooling in stage 14 is provided by withdrawing propane vapour therefrom, compressing it in compressors 52, 54, liquefying it in heat exchanger 55 then expanding it through valve 56 into a receiver 57, a liquid/vapour stream from the latter being supplied to the inlet of compressor 54. Liquid propane from the receiver is further expanded in valve 32 and supplied to stage 14. The incoming sea water in line 15 may be additionally pre-cooled in heat exchanger 58 which is supplied with liquid propane from receiver 57 through line 59, the propane being returned to the intake of compressor 52. The output streams 29 and 17 of the process may be used to cool propane in heat exchanger 55, which may also be cooled by sea-water not used in the process, and seawater in line 15. Temperature and pressure conditions for the process are specified. In a modification (Fig. 1, not shown) only a single hydrate-forming vessel is employed.