Process for stabilizing silica-rich geothermal brine to prevent silica scaling

A continuous silica removal process for reducing the dissolved silica content of silica-rich geothermal brine also containing ferrous ions and having a pH of about 4.5 to 6.0, so as to enable substantially silica scale-free reinjection of said geothermal brine flow, said process comprising the steps of:

• (a) continuously providing a supply of ferric ions, including contacting said ferrous ions in said brine with an oxidizing agent so as to oxidize at least a portion of said ferrous ions to ferric ions;
• (b) continuously allowing said ferric ions to combine with said silica dissolved in said geothermal brine so as to lower the pH of said geothermal brine and form an insoluble, iron-rich siliceous material;
• (c) continuously separating said insoluble, iron-rich siliceous material from said geothermal brine flow so as to form a stabilized geothermal brine flow having a reduced dissolved silica content and a pH of about 3 to 5;
• and
• (d) controlling said providing of ferric ions said allowing of said ferric ions to combine with said dissolved silica and said continuously separating of and insoluble, iron-rich siliceous material from said geothermal brine flow so as to cause the dissolved silica content of said stabilized geothermal brine to be below a preselected silica level assuring substantially silica scale-free injection of said stabilized brine flow.

A continuous silica removal process for reducing the dissolved silica content of flashed geothermal brine from a geothermal brine power plant, said geothermal brine being still under pressure, being supersaturated after flashing with amorphous silica and having a substantial ferrous ion content and a pH of about 4.5 to 6.0, said process comprising the steps of:

• (a) injecting air into said geothermal brine just upstream of an atmospheric separator, so as to oxidize a portion of said ferrous ions to ferric ions;
• said ferrous ion to ferric ion oxidation being caused to occur within a preselected time after said brine becomes supersaturated with silica;
• (b) discharging said flow of aerated geothermal brine into said atmospheric separator, so as to additionally flash and brine to substantially atmospheric pressure, whereby releasing low pressure steam from said brine;
• (c) discharging said flow of aerated geothermal brine from said atmospheric separator into a clarifier tank and allowing said ferric ions to combine with said amorphous silica in said geothermal brine so as to lower the pH of said geothermal brine and form insoluble, iron-rich amorphous siliceous materials;
• (d) allowing said insoluble, iron-rich amorphous siliceous materials to precipitate in said clarifier tank so as to form a stabilized geothermal brine having an amorphous silica content reduced to a level preselected for enabling substantially silica scale-free reinjection of said stabilized brine and a pH of about 3 to 5;
• (e) discharging a flow of said stabilized geothermal brine from said clarifier tank for reinjection through at least one reinjection well into a subterranean formation;
• and
• (f) removing said insoluble iron-rich amorphous siliceous material from said clarifier tank.

A silica removal process for reducing the dissolved silica content of geothermal brine supersaturated in silica, said geothermal brine also containing ferrous ions and having a pH of about 4.5 to 6.0, said process comprising the steps of:

• (a) aerating said geothermal brine so as to oxidize at least a portion of said ferrous ions contained therein to ferric ions;
• (b) allowing said ferric ions to combine with said silica in said geothermal brine so as to lower the pH of said geothermal brine and form insoluble, iron-rich siliceous material;
• (c) separating said insoluble, iron-rich siliceous material from said geothermal brine so as to form a stabilized brine having a reduced silica content, of a pH of about 3 to 5;
• and
• (d) controlling said steps (a), (b) and (c) so as to cause said stabilized brine to be non-supersaturated in silica.

A silica removal process for reducing the silica content of geothermal brine having a pH of about 4.5 to 6 after said geothermal brine has become supersaturated in silica, said process comprising the steps of:

• (a) providing a supply of ferric ions to said geothermal brine;
• (b) allowing said ferric ions to combine with silica in said geothermal brine so as to lower the pH of said geothermal brine and form insoluble, iron-rich siliceous material;
• (c) separating said insoluble, iron-rich siliceous material from said geothermal brine so as to form a stabilized brine having a reduced silica content and a pH of about 3 to 5;
• and
• (d) controlling steps (a), (b) and (c) so as to remove sufficient silica from said geothermal brine to cause said stabilized brine to become non-supersaturated in silica for all brine injection conditions within less than about two hours after said brine has become supersaturated in silica, said controlling step including controlling step (a) so as to provide said ferric ions within less than about 15 minutes after said geothermal brine has become supersaturated in silica.