Silica scale inhibitors
Industrial water such as in a geothermal unit is stabilized against silica polymerization and flocculation by using a combination of inhibitors including a nonionic polyether and a monomeric polycarboxylate.
1. A method of inhibiting the formation of silica scale in a geothermal system, comprising treating the water in the geothermal system with an anti-scalant effective amount of a combination of two inhibitors comprising a first inhibitor and a second inhibitor, wherein the first inhibitor comprises polyethylene glycol having a minimum molecular weight of 2000 g/mol and wherein the second inhibitor comprises EDTA or pentetic acid.
2. The method according to claim 1 , wherein the second inhibitor comprises EDTA.
3. The method according to claim 2 , wherein a combination of two inhibitors has a polyethylene glycol to EDTA weight ratio of 1:2.
4. The method according to claim 1 , wherein the first inhibitor comprises PEG 9000.
5. The method according to claim 1 , wherein treating the water comprises forming treated water, and wherein a concentration of the first inhibitor in the treated water is from about 0.1 ppm to about 100 ppm, and a concentration of the second inhibitor in the treated water is from about 0.1 ppm to about 100 ppm.
6. The method according to claim 1 , wherein the pH is 7 to 8.
7. The method according to claim 1 , wherein the first inhibitor has a weight average molecular weight of 3800 to 20000 Dalton.
8. The method according to claim 1 , wherein the second inhibitor is pentetic acid.
9. The method according to claim 1 , wherein the water in the geothermal system comprises 20 ppm to 1000 ppm silica as SiO 2 .
10. The method according to claim 1 , wherein the polyethylene glycol has a weight average molecular weight of at least 4000 Dalton.
11. The method according to claim 1 , wherein the polyethylene glycol has a weight average molecular weight of at least 5000 Dalton.
12. A method of inhibiting the formation of silica scale in the water of a geothermal system, comprising treating the water of the geothermal system with an anti-scalant effective amount of a combination of two inhibitors consisting of a first inhibitor and a second inhibitor, wherein the first inhibitor comprises a polyethylene glycol having a molecular weight of at least 2000 g/mol and the second inhibitor comprises EDTA, pentetic acid, or salts thereof.
13. The method according to claim 12 , wherein the water in the geothermal system comprises 1 ppm or more of Al 3+ .
14. The method according to claim 12 , wherein the water in the geothermal system comprises 20 ppm to 1000 ppm silica as SiO 2 .
15. The method according to claim 12 , wherein the first inhibitor comprises polyethylene glycol with a number average molecular weight of at least 3800 g/mol.
16. The method according to claim 12 , wherein the first inhibitor comprises polyethylene glycol with a number average molecular weight of at least 4000 g/mol.
17. An aqueous composition stabilized against silica polymerization and flocculation comprising water and silica, and further comprising stabilizing amounts of a first inhibitor comprising a polyethylene glycol having a molecular weight of at least 4000 g/mol and of a second inhibitor comprising EDTA or pentetic acid.
18. The aqueous composition according to claim 17 , further comprising 1 ppm or more of Al +3 .
19. The composition according to claim 18 , comprising 0.1 to 100 pm of the polyethylene glycol and 0.1 to 100 ppm of EDTA.
20. The composition according to claim 17 , comprising 200 ppm to 1000 ppm of SiO 2 .