Hydrothermal Dissolution of Granitic Rock in Fluidized Tube Reactor in a Temperature Gradient.
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概要
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Laboratory experiments reacting granite with pure water by fluidized tube reactor with temperature gradient have been carried out, in order to simulate water/rock interactions during heat extraction from a Hot Dry Rock (HDR) geothermal system. The tube reactor (1000mm long) was packed with cylindrical granite samples. The inlet temperature was 220°C and the maximum temperature set to be 350°C at the 65 cm downstream from the inlet. The experiments lasted for 20 days in maximum at about 20 MPa and a constant flow rate (0.29 cm/min). Chemical composition of the output solutions was monitored during the experiments. Si concentration was almost unchanged through the experiments (315 ppm on the average). Na, K and Al concentrations became stable after 168 hours at about 6.5, 2.9 and 4.3 ppm respectively. No considerable change of pH was observed (ca. 7.4).The reacted rock samples were divided into four zones from their weight loss/gain behavior. Zone I was located 2 to 18 cm downstream from the inlet and the reaction temperature ranges from 220°C to 275°C, zone II 18-58cm (275-345°C), and zone III 58-72 cm (345-350°C) and zone IV 72-96 cm (350-345°C). The changes of the weight loss/gain of each zone with time were approximated with straight lines. The dissolution of granite was dominant in zones I, II, IV and the weight gain was observed in zone III as a result of the precipitation of new secondary minerals. The apparent dissolution rate was maximum in zone II that was 1.7 times as large as that in zone I and 2.9 times of that in zone IV. The results of the laboratory experiments about water/granite interation processes with a temperature gradient from 220°C to 350°C could be summarized as follows: The rock is dissolved in the injection fluid with increasing temperature, the dissolution rate of rock reaches the maximum in 275°C-345°C, and the precipitation takes place suddenly at 350°C.
- 日本地熱学会の論文
日本地熱学会 | 論文
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