2022 Volume 44 Issue 2 Pages 85-96
As for the influence of the water vapor emitted from the cooling towers on the vegetation around the geothermal power plants, there is a general concern about damage to tree crowns caused by ice accumulation in winter. In order to clarify the occurrence of icing and the meteorological conditions (temperature, wind speed, humidity) at the time, we conducted a field experiment that were placed each pseudo tree with set up a beech (Fagus crenata) sapling and three wooden round bars (1 cm, 2 cm, and 5 cm in diameter), at distances of 20 m, 30 m, and 60 m from the cooling towers on the downwind side of the main wind direction. The experiment was conducted from November 28, 2019 to March 14, 2020. As a result, we confirmed the occurrence of icing, mainly rime, by the water vapor emitted from the cooling towers. The meteorological conditions in which icing occurred were generally when the temperature was below -2°C and the rate increases with decreasing temperature, the relative humidity was above 70%, and the wind speed was above 1 m/s. The ice growth rate was generally less than 2 to 3 mm/hr, though the maximum was about 10 mm/hr on wooden round bars 1 cm diameter on the pseudo tree at 60 m distance. It took about 24 hours when ice grew significantly. In our experiments, the thickness of ice tended to increase with distance from the cooling towers and with the smaller diameter of the wooden round bar, the maximum thickness was 9.5 cm on the 1 cm diameter round bar attached to the pseudo tree at the furthest distance (60 m) from the cooling towers. However, thickness of the ice did not develop continuously, caused by melting due to increase in temperature and falling due to strong winds. In this experiment, no stem breakage of the beech saplings occurred, even though the stems were bent by more than 90 degrees due to icing of 1 to 1.5 cm on the 1 cm diameter round bars. Although the results obtained in this study are limited to a single site, they are valuable for considering environmental considerations for future geothermal power plants, such as meteorological conditions and icing characteristics.
