Patent GB-1052034-A (GB)
IPC: C02F1/04
Filed: 1963-06-07
Abstract: 1,052,034. Acidifying sea water by electrodialysis. AMERICAN MACHINE & FOUNDRY CO. June 7, 1963, No.22799/63. Heading C7B. Apparatus for electrolytically producing acid for use in treatment of salt water, e.g. sea water, comprising a cell having an anodecontaining compartment a salt water compartment and a cathode-containing compartment with a cation permeable membrane between anode and salt water compartments and an anion-permeable membrane between the salt water and cathode compartments, separate first and second circulating means for circulating an acidified liquid and an aqueous alkaline liquid through said anode and cathode compartments, and a floe former, said second circulating means including an alkaline solution tank having an overflow leading into the floe former. As shown, acid for addition to sea-water fed to an evaporator in a ship to prevent scale formation is formed in an electrodialysis cell comprising anode, acidforming, buffer and cathode compartments formed by hollow end plates 14, 15 and frame members 16, 17 separated by cation permeable membranes 20, 22 and an anion permeable membrane 21. Dilute sulphuric acid is circulated through the anode compartment in which oxygen is evolved and the anolyte is kept at constant strength by a float valve-controlled addition of distilled water. The acid forming compartment is fed with sea water which after acidification is mixed with the main feed via a venturi blender 29 pipe 12 to the evaporator. Softened sea water and alkaline, sea water are passed through the buffer and cathode compartments, the feed for them originating from a floe settling tank 61 in which insoluble magnesium and calcium carbonates are removed from sea water supplied via pipe 57. Either this supply pipe or the floe forming cup 59 are heated while  the settlement tank is lagged. Carbon dioxide in addition to that present in the sea water initially supplied may be introduced into the tank 48, such additional CO 2  being obtained by stripping from the acidified sea water product. Hydrogen evolved in the cathode compartment is withdrawn through pipe 52 with the catholyte and separated from it by a blower 56 from which the hydrogen is ducted to waste. Modifications providing a constant head supply instead of control by valve 58 is also described and the settling tank 61 may be omitted if an overflow for the floc forming cup 59 is provided, although rinsing of the buffer and cathode compartments is then necessary before prolonged shut-down. By effecting hydraulic and electrical reversal Fig. 3 (not shown), flushing of the cell may be effected periodically to remove any traces of scale. If reversal is not required the buffer compartment 17 and associated pipes and tank 40 may be omitted, pipe 68 feeding directly into tank 48. To increase acid production capacity without increasing ionic membrane sizes or multiplying electrical connections, several sets of four compartments may be arranged end-toend separated by bipolar platinum foil electrodes with compartments of the same function being connected in series, the end compartments of the cell alone containing electrodes to which the D.C. supply is connected.