和嶋 隆昌

We attempted to desalinate surface seawater from Imari Bay using an upward spray flash seawater desalination plant. Considering that the rise in the boiling point caused the nonvolatile solutes in seawater, the evaporation phenomenon with seawater was almost the same as that with tap water, and a sufficient desalination ratio was confirmed. The principle components of seawater and B were removed from the product water, and the product water had a high purity of <0.5 mS/m.

海洋深層水からのリチウム回収を目的としてパラオおよびフィジー海域における海水中のLi⁺分布の調査およびLi⁺回収において妨害となる海水中の主要イオン分布の調査を行った.両海域の各地点においてLi⁺濃度は約0.15-0.16mg/Lの一定濃度で鉛直方向に分布していた.海水中の主要共存イオンであるNa⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-, Br^-, SO₄^2-についても同様に鉛直方向に一定であった.これらの海域の海水は実証試験に用いた伊万里湾表層水の化学組成とほぼ等しかった.実証試験に用いたλ-MnO₂吸着剤は, 低温である海洋深層水から表層海水よりも効率的なLi⁺吸着を示した.これらのことより, パラオおよびフィジー海域中には, Li⁺及び共存主要イオンはほぼ一様の分布をしており, 低温のパラオおよびフィジーの海洋深層水から, λ-MnO₂吸着剤を用いて効率的なリチウム回収が期待できる.

上向き噴流式フラッシュ蒸発海水淡水化装置において, 口径が異なるステンレス製直管型ノズルを用いて実験を行い, ノズル口径が蒸発現象に与える影響を調べるとともに, 1本のノズルからの噴流の影響範囲を予測する無次元整理式を求めた. 実験はノズル流出液温度をT_o=24-35℃, ノズル内平均液流速をυ=1.2-2.7m/s, 過熱度を△T_s=2.0-6.OKに設定して行った. 噴流の温度は, 水平に並べた10本の測温抵抗体を高さ方向に移動させて合計25カ所で計測した.<BR>その結果, ノズル口径が大きいほど圧力損失が小さいため, 過熱域がノズル出口からと流側へ拡大し, 配管およびノズル内壁に生成した気泡が, ノズルから噴出するまでにより大きく成長して蒸発が促進された. また, 実験データから, 蒸発終了高さz_hならびに半径方向蒸発終了距離γ_eに関する無次元整理式を導出した. これらの式を用いることにより, 実プラントの設計に必要とされるフラッシュ蒸発器の高さならびにノズルの設置間隔を, 運転条件に応じて見積もることができる.

In the Pacific island nations, Ocean Thermal Energy Conversion (OTEC) system is particularly sought after since the said region is seriously threatened by rising sea level as a result of climate change. In order to draw up the most suitable OTEC system for individual needs, it is imperative for us to have as much as detailed oceanographic information. There have been, however, very few and only limited data of the region available. Under these circumstances we have undertaken in December 2003 our own research and investigation works in the Fijian waters. The renowned ocean research vessel "Koyomaru" of National Fisheries University, Japan was placed at our disposal for the investigative works. This paper deals with not only the results of investigation and our subsequent evaluation of the research works but also the comparison of two different data, one in the Fijian waters and the other in the waters of Palau Republic, another Pacific ocean islands nation, for further clarification of the potentiality in Fiji of OTEC system for multiple utilization of ocean energy.

In a geothermal power station, silica scale often causes serious problems, such as a decline of the heat exchanger's performance, and plugging of pipelines and permeable layers. Polymerization of silicic acid dissolved in geothermal water plays an important role in silica scale formation, and this reaction is affected by many factors, such as temperature, pH, silica concentration and coexisting elements. In this study, the effect of residence time, temperature, aluminum concentration, and pH on silica precipitation was investigated to resolve silica scale troubles. The experimental results were as follows : Polymerization of silicic acid supersaturated in geothermal water progressed by decreasing temperature and increasing residence time. The aggregation through the formation of Si-O &middot;&middot;&middot;Al ³⁺ &middot;&middot;&middot;O-Si bonds occurred in the narrow pH range between 4 and 5. A large quantity of silica precipitation formed by adding trace amounts of aluminum. We present a new process of silica removal from geothermal water based on the optimum conditions obtained by experiments.