| Abstract |
The brine fluids in geothermal power plants usually have high levels of scale forming minerals within them. Typically calcium carbonate has been the key issue in the past as it is prone to precipitate out into the production well due to high temperatures, usually in the zone below the wellhead. Control of calcium carbonate is relatively straight forward and a number of established chemical control methods are available based on either phosphonate or polymer technologies. They key to successful control is having a product with suitable thermal stability to withstand the conditions within the production well and inhibit calcium carbonate deposition. More recently, with the drive to extract ever more useful heat energy from the brine, silica deposition is becoming more of an issue. The reason for this is that as the brine temperature is lowered because of additional heat extraction prior to reinjection, there comes a point where silica levels exceed their solubility. As a result, the silica will polymerise forming colloidal silica, which will then precipitate from solution either as silica or as the metal silicate. Either precipitation can be exceedingly damaging. The glassy deposits can greatly impair heat transfer, reducing plant efficiency. Removal of such deposits is difficult and often the only solution is to clean with hydrofluoric acid which is not an easy task due to safety concerns. This paper considers the use of a thermally stable polycarboxylic acid (PCA) polymer, to not only control calcium carbonate based deposits in the wellhead, but also prevent the precipitation of metal silicates within the heat exchangers as the brine is progressively cooled. The use of these materials offers an enhanced level of plant protection, improving power output and minimising plant downtime. In addition, PCA based polymers contain extremely low levels of phosphorus, helping to minimise impact on the environment following discharge. |