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

对于地热能利用系统的发展，建立传热表面结垢或结垢的防治技术是一个重要而紧迫的问题。本课题以化学工程方法分析了结垢机理的基本数据，提出了防治技术、种子添加法和超声波辐照法。为了有效地应用加籽法，对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，观察了单二氧化硅和多二氧化硅的吸附率。结果合理地表明，聚合过程的活化能为5 ~ 8 kcal/mol，受存在的金属离子的影响。这些数据可为种子添加技术的设计提供参考。本文还提出了一种超声波辐照技术，以防止传热表面结垢。在实验中，铜管浸入硫酸钙水溶液中，热水在管内流动。对管道表面沉积的水垢质量的测量表明，在没有超声波照射的情况下，沉积速率显著提高。超声照射下，未见鳞屑形成。在采用间歇辐照技术的情况下，发现在水垢成核期进行辐照对防止水垢沉积更为有效。研究结果的详细内容将发表在2004年第30卷的《日本科学学刊》上。在地热能源利用方面，对将广泛用于地热流体和（或）能源输送的灯芯进行了实验表征。通过对网芯毛细管吸力电位的测量，建立了一个毛细管模型，合理地考虑了扭曲度与饱和水平的关系，从而可以预测非饱和导电性，并推导出无因次的毛细管吸力电位。毛细管模型也被用来预测在灯芯中观察到的饱和剖面，在灯芯中液体以恒定的渗透速率流过并排出到一个液台。由观察到的毛细电势确定的摩擦因数与雷诺数Re有一个简单的关系，实验证明该关系与编织网的类型和由芯组成的网层无关。摩擦系数与雷诺数的乘积验证了该方法对预测网格型芯层饱和导水率的有效性。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