| Abstract |
Recently, several small binary systems are installed at high temperature hot spring field. For example, the production test using small Kalina system is carried out at Matsunoyma hot spring field. And the power generation using small binary system using hydrofluorocarbon is installed at several hot springs in Kyushu Island. One of the problems with this system is corrosion and scaling on the plates of the heat exchanger in the binary system. This problem is similar to the corrosion and scaling that occurs in standard geothermal system. In order to investigate this system, estimation of scaling and corrosion of a heat exchanger is being carried out at several hot spring fields. First, the scaling and corrosion test was carried out at the Otari test site. The fluid has high T-HCO3, Cl and SO4 concentration with pH 7 and a temperature of 70 ºC. In the hot spring water path, sulfide minerals were deposited on a Cu plate and iron reacted with CO2. Aragonite, calcite and silica precipitated in the heat exchanger. However in the cooling water path, aragonite precipitated especially in the high temperature area due to super-saturation by heating. For the second test, at Matsunoyama field, we estimated the possibility of scaling in the system by calculating the equilibrium of silicate minerals and carbonate minerals using Solveq-Chiller, developed by Reed (1982). The test well at Matsunoyama, Takanoyu#3, has a high Cl concentration of about 9,000 mg/l, about 3700 mg/l Na, 200mg/l K, 2,100 mg/l Ca, 0.4 mg/l Mg and 36 mg/l HCO3. During the cooling process of hot spring fluid from 100 to 40 ºC, in the heat exchanger, quartz and calcite become supersaturated, but other minerals such as dolomite, amorphous silica, talc and tremolite are under-saturated. Thus we estimated that the scale problem will not be so serious because silica scaling (usually occurring as amorphous silica) is not expected as silica is under-saturated over 40 ºC at Takanoyu#3 and the super saturation of calcite decreases with decreasing temperature. One of the reasons for the low risk of scaling is the low HCO3 and Mg concentrations at Takanoyu#3. |