In my laboratory, we are conducting microstructural analysis of the scale formed in geothermal power plants and hot spring hot water pipes. In particular, we focus on the materials that are formed at the earliest stage for geothermal fluids and hot spring water pipes.
Crystal structure (which mineral does it resemble?)
Molecular structure (which bonds, such as Si-O bonds, are abundant?)
The following is a detailed description of our research. The following is a detailed description of our research. The paper on microstructure analysis is currently being written and cannot be published, so it will be added soon.
Scale and geothermal power generation
Geothermal power generation is difficult to operate in a stable manner, and although geothermal power plants are constructed, their actual capacity may be much lower than expected. One of the major obstacles to such stable operation is scale, which causes pipe blockage and reduced heat exchange. Scale is a substance deposited on the pipes that transport geothermal water (Fig. 1). If left unattended for a long time, scale will grow and clog the pipes. One of the major problems is that the unit price of electricity generated (price of electricity) increases due to the maintenance cost and the decrease in the amount of electricity sold during the maintenance.
Fig. 1 Photographs of pipe and heat exchnger with scaling. (under no treatment to water)
What is the first substance that adheres to the material surface as scale?
If the material is covered with scale, the inhibition effect is lost. Therefore, it is important to inhibit the adhesion of the mineral phase that first adheres to the material surface. In most hot spring areas, the main component of scale is calcium carbonate (JOGMEC: "Guidelines for the Design of Small-scale Geothermal Power Plants," Kitano, Y.: Journal of the Japan Society of Hot Spring Engineering, 2(1964), 45-49.), but the mineral phases that adhere to the top surface of the material are not clear. For example, Kohama Onsen in Unzen City, Nagasaki Prefecture is famous for the formation of calcium carbonate scale, but our research revealed that the mineral phase of the top surface scale of the material in Kohama Onsen is silicate. Currently, we are trying to clarify the mechanism of scale formation in geothermal and hot spring waters throughout Japan by identifying the initial materials that adhere to the surface of the materials in all types of springs.
Fig. 2 Pipe with scale formation sampled at Kohama Onsen, Unzen City, Nagasaki Prefecture (the piping in Fig. 1(a) was cut for analysis).
Establishment of a method to imitate scale
As mentioned above, we have been analyzing the crystal and molecular structures of scales collected from actual geothermal power plants and hot spring areas. In my laboratory, we are trying to simulate the same structure as the collected scale in the laboratory. Currently, the only way to confirm whether a material or a chemical is effective in inhibiting scale is to visit the site and actually use it. However, such a situation slows down the speed of research and development. Therefore, Morita and Yamaguchi developed a device to simulate the field scale. By using this device, we can simulate the structure close to the local scale, which is expected to speed up the R&D. Currently, we are conducting research and development to improve the simulation of the field scale.
Fig. 3 Field scale simulator