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

在地热能利用系统的发展中，建立防止传热表面结垢的技术是一个重要而紧迫的问题。本研究从化学工程的角度分析了结垢的形成机理，提出了防垢技术、种子添加法和超声波法，并对种子添加法的结垢机理进行了详细的探讨。通过改变pH值、温度和初始二氧化硅浓度，从单二氧化硅和多二氧化硅浓度的测量中观察吸附速率。结果合理地表明，聚合过程的活化能为5-8kcal/mol，并受金属离子的影响。这些数据可用于种子添加技术的设计，并提出了一种超声辐照技术， ...更多信息 防止传热表面上的水垢沉积。在实验中，将铜管浸入硫酸钙水溶液中，并在管内流动热水。测量沉积在管道表面上的水垢的质量，表明在没有超声辐照的情况下具有显著的沉积速率。另一方面，在超声波照射下，没有观察到结垢。在间歇辐照技术的情况下，发现在氧化皮成核期间的辐照对于防止氧化皮沉积更有效。所获得的结果的详细内容将发表在《科学研究综述》（第30卷，2004）中。在地热能利用方面，对将广泛用于地热流体和/或能量输送的芯进行了实验表征。通过对网孔式吸液芯毛细吸力势的测量，建立了一个毛细模型，该模型考虑了吸液芯弯曲度对饱和度的依赖关系，从而合理地预测了非饱和导水率，并推导出了无量纲毛细吸力势。毛细管模型也已被提供来预测在吸液芯中所观察到的饱和剖面，通过该吸液芯，液体以恒定的渗透速率流动并排出到液体table.由所观察到的毛细管势确定的摩擦因子与雷诺数Re通过一个简单的关系，实验证明该关系与由吸液芯组成的网格编织类型和网格层无关。计算结果表明，该方法可用于预测网状吸液芯的饱和导水系数。研究结果发表在日本化学工程杂志（2003年第36卷）上。少

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