Patent GB-1005823-A (GB)
Title: Improvements in process for the conversion of salt water to fresh water
IPC: C02F1/22
Filed: 1962-10-08
Abstract: 1,005,823. Purifying salt water by freezing. W. C. RICH Jr., and D. M. BRADT. Oct. 8, 1962 [Oct. 10, 1961], No. 38050/62. Heading F4H. A process for obtaining fresh water from salt water comprises freezing water from the salt water on to the surface of water insoluble particles or droplets cooled below the freezing point at which ice crystallizes from the salt water, removing the ice coated particles and washing them of residual traces of salt water, melting the ice coating, and separating the resultant fresh water. In a continuous process as shown, Fig. 1, salt water which has been precooled by heat exchange with either fresh water or concentrated salt water resulting from the process enters a freezing zone 2 of the apparatus through a pipe 1. A liquid refrigerant which is immiscible with water is fed into the freezing zone through a pipe and nozzle assembly 5, evaporation of the refrigerant removing heat from the salt water, so that ice forms on the surface of cooled solid particles 3 introduced through a pipe 4a. The ice coated particles sink slowly into a washing zone 7 where fresh water is supplied through a pipe 9 at a rate sufficient to prevent salt water from passing from zone 2 into zone 7. The washed ice coated particles 8 and the washing water pass down into a melting zone 10 where compressed gaseous refrigerant injected through a nozzle assembly 11 condenses and supplies heat to melt the ice coatings. The particles 3 sink into the lowest zone 14 of the apparatus. The condensed refrigerant collects in the upper part of the lower vessel of the apparatus, and is drawn off through a pipe 27 by a pump 28, to be supplied to the nozzles 5 and in small quantities through a pipe 29 into the pipe 4a, where it evaporates to cool the particles 3 before they enter the freezing zone 2. A refrigerant compressor 20 supplying the nozzles 11 also supplies gaseous refrigerant to a pipe 23 discharging into the lower part of a riser 22, to lift particles 3 and fresh product water to a cyclone separator 4 after the manner of an air lift. The cyclone contains a peripheral mesh through which the water passes to a pipe 23a for recovery, while the refrigerant gas leaves through a pipe 24, the particles 3 dropping into the pipe 4a. A compressor 25 passes the refrigerant into a suction line 19 of the compressor 20 which line carries refrigerant gas from above the freezing zone to the compressor 20. Uncondensed refrigerant from the melting zone collects in a space 16 for withdrawal through a pipe 17. Concentrated salt water is withdrawn from the freezing zone 2 through a pipe 30. In the apparatus of Fig. 2, the melting zone 32 is provided with a deflector tray 31 and baffles 33. In the zone 34, a deflector plate 38 directs fresh water, which is denser than the refrigerant liquid, through a mesh 35 to sink to a zone 36, from which the water is pumped to a recovery plant, through pipe 34a, and to the washing zone, through pipe 9. The particles 3 move down the mesh 35 to a collector 37 below the deflector 38, which latter ensures that the liquid in the collector is refrigerant only. The compressor 25 maintains a pressure in the riser 39 sufficiently low for the liquid refrigerant therein to boil, the gas bubbles lifting particles 3 up to the cyclone 4. In this system, the particles are cooled in the riser 39. A system for the use of droplets of a liquid, e.g. mercury (Fig. 3, not shown), as the nuclei for freezing includes a tank for the liquid, which latter is cooled in the tank by the evaporation of liquid refrigerant supply by the pump 28. The liquid is sprayed from a nozzle above the freezing zone to form droplets 3. These droplets finally collect and coalesce in the lowest zone of the apparatus, and are pumped back to the cooling tank.