| Abstract |
In this paper, we summarize research on the scaling at the Obama Onsen binary power plant. To prevent scaling in the geothermal plant, we have been developing a surface treatment to mitigate calcium carbonate, which mainly comprises the scale in the Obama hot spring. We aimed to utilize eluted ions from the coating. In laboratory tests, Ni-P coating exhibited the greatest prevention of scaling because eluted phosphate ions were shown to inhibit calcium carbonate crystal growth. The scaling test was conducted in a field environment for approximately five months. Carbon steel plates with Ni-P plating and stainless steel pipes were installed as transport pipes. However, the scaling propensities among them were similar, and the anti-scaling effect of Ni-P plating did not work in the field environment. To clarify this, we analyzed the microstructures of the scale and proposed a basic microstructure. The scale constituted a layered structure; initially, the surface of the steel pipe was covered with corrosion products, which were subsequently layered with magnesium silicate. The phase of the initial scale was not calcium carbonate but magnesium silicate. Therefore, Ni-P plated steel does not appear to exhibit an anti-scaling effect. Based on these findings, we are studying the mechanism of scale formation on materials and establishing a method for mimicking scale in laboratory tests to investigate the anti-scaling properties of materials. |