| Abstract |
Solid deposition of minerals from geothermal waters has been identified as a primary constraint in the operation of high temperature geothermal fields for electric power generation. The 20 years operating experience of the Palinpinon-I geothermal production field has shown that mineral deposition, particularly amorphous silica, in well bores and surface pipelines can lead to costly removal operations, lengthy decomissioning periods, and, in certain cases, causing total power plant trips. This paper attempts to provide an interpretation on the physico-chemical mechanism of amorphous silica deposition, through a comprehensive correlation of fluid chemistry, field inspection data, operating parameters, and engineering design of the Fluid Collection and Disposal System (FCDS) of the Palinpinon-I geothermal production field, from 1984-2001, enable a better understanding of this phenomenon, and further minimize the associated operating problems. The latest inspections indicate a reduced annual deposition rate of 8-19 mm in the cross-country reinjection lines of zero inclination, compared to earlier values. Correlation calculations reveal that fluid chemistry, line separation temperatures, flow regime, fluid velocity, and line gradient of the separated brine are the critical factors which influence the rate of amorphous silica deposition. Mechanical well work-over and acid injection, line scale removal also by mechanical method, installation of deposition spools in long brine lines of zero gradients, relocation of vessel isolation valves, and re-orientation of two-phase line interconnections, have been adopted as remedial solutions only. For future engineering design, drastic increases in diameters of interconnected pipes, zero inclination of cross-country brine lines over long lengths, line fluid velocities of less than 2.0 m/sec, and partially-liquid filled operation of the brine lines, should be avoided. |