Problems of two-phase geothermal fluids : Flow characteristics and scaling in pipes
An experimental study of horizontal annular air/water flow was carried out in a new 50 mm ID pipeloop. At high gas flow rates the liquid distribution tended to become axisymmetric, while at lower rates the influence of gravity was very significant, resulting in a thick liquid layer at the pipe bottom. Scale from the Milos geothermal plant was studied by X-ray diffraction, elemental analysis and scanning electron microscopy. The scale consists of heavy metals (Pb, Zn, Fe, Cu), sulphur and silicon compounds, which account for 90-100% of the deposited mass. A silicon-rich layer adheres to the metal surface, even in places where sulphides are the main constituents of the scale. Experiments to study PbS deposition were carried out under conditions resembling the sudden supersaturation of geothermal fluids upon flashing. Deposition rate and deposit morphology were strongly dependent on pH and the initial deposition rate was linearly dependent on the flow rate, suggesting that PbS deposit formation is a diffusion controlled process. It is concluded that pH modification is the most effective way to control scale in geothermal installations. Scale may also be controlled by the use of crystal growth inhibitors, by the careful design of geothermal plants and by the maintenance of appropriate operating conditions.
Bibliographic Reference: EUR 13320 EN (1991) 26 pp., MF, ECU 4
Record Number: 199110020 / Last updated on: 1994-12-02
Original language: en
Available languages: en