Scale deposition in wells and in pipes on the surface has been a serious problem for geothermal power plants as the effective method for removing the scales or for preventing the scales from being deposited has not been established yet. In this study, in order to clarify the performance of high speed water jets in removing geothermal scales, fundamental experiments were carried out for three kinds of geothermal scales, a calcium carbonate scale and two silica scales, which were deposited in transportation pipes. Slot cutting in water was conducted first to know the effect of driving pressure and standoff distance, and then removal of the scales with rotary nozzles was tested to clarify the effect of rotary speed, rate of feed and driving pressure. As a result, it is shown that high speed water jets can remove geothermal scales almost perfectly without damaging the pipe if sufficient driving pressure is employed, and that optimum rotary speed gives the largest rate of removal. The test results also show that the driving pressure required to remove the scales is roughly proportional to the tensile strength of the scale, and that larger size of 5 to 15 mm is predominant in particle size distribution of removed scales.
This paper describes a fundamental study of effects of phase-change on water-steam flow through a porous medium. The experiments are carried out by using a packed glass beads bed submerged horizontally in a thermostat kept the temperature higher than 373K. The experimental results are compared with the calcu-lation based on a one-dimensional two-phase model which has a new fitting parameter C in the empirical equation relating the relative permeability for a non-wetting phase to the saturation. The parameter C indicates a critical point at which a wetting phase starts to obstruct a non-wetting phase flow through domi-native paths in a porous medium. The conclusions are as follows: (1) There exists 'Jamin effect' in the water-steam flow with phase-change, which is an obstructive effect of gas bubble on the gas and liquid flows through a porous medium.(2) The relative permeability curve of non-wetting phase, including the new fitting parameter C, almost agrees with the relationship between water saturation and the relative permeability of gas proposed experi-mentally by Wyckoff et al. (1936).(3) The proposed mathematical model describes water-steam flow with phase-change in the region of which the steam ratio is smaller than 0.6.
A mathematical model which simulates the previously reported experimental results on permeability decrease of porous media is proposed. In the model, the silica deposition rate is proportional to the product of the degree of supersaturation of dissolved silica in geothermal water with respect to amorphous silica solubility and the surface area of porous media exposed to the water. In addition, the effect of the previous-ly deposited silica on silica deposition should be considered because it accelerates the silica deposition. Unknown deposition rate coefficients, β1 and β2, are determined using trial and error method so as to fit the measured flow rates. The calculated profiles for the amount of deposited silica and permeability are then compared with the experimental data. The optimum values for the deposition rate coefficients are obtained by assuming that a very small quantity of excess silica in the water can deposit along the porous media. For instance, at the inlet of the porous media, it is only 2 ppm, although the concentration of excess silica in the water is as high as 201 ppm. The deposition rate coefficients determined are β1=3.5x10-4 cm/s and β2=4.0x103∼5.0x103
Infrared measurements by a helicopter-borne remote sensing system were conducted in the nineteen volcanic and geothermal fields in Kyushu, south western Japan. Heat discharges calculated from the thermal images by a method based on heat balance of the ground surface range from 2.0 × 105 cal/sec (for a weak steaming ground) to 2.1 x 107 cal/sec (for a crater of an active volcano). Finally, it is found that average heat fluxes are approximately constant, 104 HFU.
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