Speculations are presented as to the mechanism of inhibition of silica precipitation and recommendations for further testing of these additives. The best additive formulation for the brines of the Salton Sea Geothermal Field appears to be a mixture of one of these silica precipitation inhibitors with a small amount of hydrochloric acid and a phosphonate crystalline deposit inhibitor. Other promising compounds are PAE HCl (Dynapol poly(aminoethylene, HCl salt)), which also somewhat reduces the 220/sup 0/C scale Ethoquad 18/25 (Armak methyl polyoxyethylene(15) octadecylammonium chloride) and Mirapol A-15 (a Miranol Chemical polydiquaternary compound). It had no effect on the scale at more » 220/sup 0/C, but it reduced the scales at 125 and 90/sup 0/C by factors of 4 and 18, respectively, and it also has activity as a corrosion inhibitor. The best single compound was Corcat P-18 (Cordova Chemical Co. Three of these and certain combinations of compounds were then given a 40-h test to determine their effectiveness in retarding scales formed at 220, 125, and 90/sup 0/C. An initial group of compounds was narrowed to four on the basis of their activity as silica precipitation inhibitors. The Lawrence Livermore Laboratory Brine Treatment Test System at Niland, Imperial Valley, California, has been used to evaluate a number of cationic polymers and surfactants as scale control agents. Proposals for future studies are outlined. Several new compounds were tested as silica precipitation inhibitors and one, PAE HC1 (Dynapol poly(aminoethylene, HC1 salt)), was found to be the most potent yet discovered. The influence of brine salinity and pH (altered with sodium hydroxide) on the distribution of monomeric silica in the flash system was examined. Additional data are reported on the reduction of scale by acidification with hydrochloric acid, and some of the effects of producing acidified brine by the addition of hydrogen peroxide were measured.
PRECIPITATE SILICA SERIES
Changes in the salinity of the brine during the test series were found to have a pronounced effect on the rates of more » precipitation of silia and scaling, and on the effectiveness of the Ethoquad as an inhibitor. Three-day scaling tests of Ethoquad 18/25 (Armak) alone (at a concentration of 25 ppM), and Ethoquad in combination with Dequest 2060 (Monsanto) showed a scaling rate reduction of 40 to 80% at 90/sup 0/C, 15 to 40% at 125/sup 0/C, and no reduction of 210/sup 0/C. The Lawrence Livermore Laboratory Brine Treatment Test System at Niland, Imperial Valley, California, has been used to evaluate a promising organic compound to the abatement of siliceous scale in brine handling equipment.
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