Scale Removing and Preventing by Using High-Frequency Electrolysis System

Abstract

Scale precipitation is problem for geothermal and hot spring system. Especially, calcite scaling occur with pH change by degassing from production fluid and temperature increasing, since the solubility of calcite become lower at higher temperature. To prevent calcite scaling at heat exchanger or pipeline, calcite removal system using high-frequency electrolysis system was developed by Reiken Co. Ltd. This system consists of a control unit and an electrode unit with three electrodes. To prevent scaling or corrosion on the electrodes, system control periodically altering the polarity of electrodes. Then, scale is collected on only an electrode cover, cathode (–) side, that surrounds the electrodes. The precipitation reaction is represented by the following equation: Ca2+ + HCO3 – + OH– ? CaCO3 + H2O. Then, this system is used to reduce the calcium in circulating cooling water. Therefore, this electrolysis system was useful to remove calcite scales in flow line. Even if super-saturation solution for CaCO3, adhered calcite scale on stainless plate in flow line dissolved and removed with pH decreasing using electrolysis system. And this system need only 50 W electric powers to work for preventing scale and it is low running cost method. And the field test of this system was carried out at Otari hot spa area, Nagano, Japan. This system was set in water tank and 50L/min flow of underground water and hot spa water. Calcite precipitated at electrode cover about 4.0 g/day from underground water and 16.9 g/day from hot spa water with higher calcium and HCO3 concentration than underground water. This system is useful to prevent scaling on heat exchanger at hot spa region.