Patent ID: 8092656

Claim:
A process for treatment of a silica-containing aqueous feed water stream using an evaporator, said process comprising: (a) providing a feed water stream containing soluble and insoluble inorganic and organic species therein, said species comprising: (I) multi-valent metal cations, (II) alkalinity, (III) at least one molecular species which is at low ionization levels when in solution at around neutral pH, said molecular species comprises silica (SiO 2 ), metasilicic acid (H 2 SiO 3 ), or orthosilicic acid (H 4 SiO 4 ); (b) removing a portion or substantially all multi-valent metal cations from said feed water stream to a non-precipitating residual level by passing said feed water stream through membrane softening equipment, or by increasing the pH to at least 10 in said feed water stream and passing the pH adjusted stream through membrane separation equipment to filter out hardness precipitate, and thereafter passing said feed water stream through a cation ion exchange system, and (c) processing the feed water stream by: (I) removing substantially all non-hydroxide alkalinity from said feed water stream; and (II) raising the pH thereof to at least 9 or higher; (d) after removing multi-valent metal ions, removing substantially all non-hydroxide alkalinity, and raising the pH of said feed water stream to at least 9 or higher, thereafter feeding the feed water stream having a pH of at least 9 or higher into an evaporator, wherein said evaporator: (I) contains a plurality of heat transfer surfaces, (II) contains a circulating high solids solution, and (III) wherein the pH of said circulating solution is maintained to at least 9, or higher; and (e) condensing the vapor produced by the evaporator to produce a distillate stream, the evaporator also producing a high solids containing blowdown stream.