Development of prevention technique for the silica scale deposition interfering with utility systems of geothermal energy

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For the development of utilization systems of geothermal energy, it is important and emergency issue to establish the prevention techniques of scaling or fouling on heat transfer surfaces. In this research project we presented the fundamental data on scale formation mechanism which has been analyzed by a chemical engineering approach, leading to the proposal of prevention techniques, seed addition method and ultrasonic irradiation method.For the effective application of the seed addition method, scale formation mechanism has been discussed in detail. Adsorption rate was observed from the measurements of mono-and poly-silica concentrations by changing the pH value, temperature, and initial silica concentration. The results reasonably indicate that the activation energy for polymerization process is 5-8 kcal/mol, which is affected by the existing metal ions. These data are available for the design of seed addition technique.An ultrasonic irradiation technique has also been proposed for t … More he prevention of scale deposition on heat transfer surfaces. In experiments copper pipes were immersed in calcium sulfate aqueous solutions, and hot water was, flowed inside the pipes. Measurements of the mass of scale deposited on the pipe surface demonstrated significant deposition rate without ultrasonic irradiation. Under ultrasonic irradiation, on the other hand, no scale was observed. In the case of intermittent irradiation technique, it was found that the irradiation during the scale nucleation period is more effective for the prevention of scale deposition. The details of the results obtained will be published in the Kagaku Kogaku Ronbunshu (vol.30,2004).In relation to the utilization of geothermal energy, wicks which will be widely used for the transport of geothermal fluids and/or energy, were characterized experimentally. Measurements of capillary suction potential of mesh-type wicks have developed a capillary model, which reasonably makes it possible to predict unsaturated hydraulic conductivity by considering the dependency of tortuosity on saturation level, as well as to deduce a dimensionless capillary suction potential. The capillary model has also been provided to predict saturation profiles observed in a wick through which liquid flows at constant infiltration rate and draining to a liquid table.The friction factor determined from the observed capillary potential has been related to Reynolds number Re by a simple relation, which experimentally proved independent of the mesh woven-types and mesh layers consisting of a wick. The estimated product of friction factor and Reynolds number demonstrates its availability to predict,the saturated hydraulic conductivity of mesh-type wicks. The results was published in the Journal of Chemical Engineering of Japan (vol.36,2003). Less