Kinematics of a Silica Particle in the Deposition to Piping of Geothermal Power Plant

The buildup of silica scale inside geothermal pipes and wells has serious impacts on the power generation efficiency in geothermal systems. There have been a large number of studies on controlling silica scale. However, silica deposition estimated by simple chemical kinetics cannot give a rational explanation of the complicated features empirically observed in laboratory and field experiments. The aim of this research is to investigate physical effects on silica particles and calculate scale precipitation rate quantitatively with a method of numerical simulation. We regarded silica scale as colloidal particles and analyzed the particle behavior by solving the motion equation of a particle. In this process, we computed the time required for the particle diffusion to the vicinity of wall surface by considering various physical reactions including hydrodynamic process, Brownian motion, particle-wall interaction, particle size, etc. In addition, we calculated the probability of particle re-entrainment from wall surface, which can be applied to CFD (Computational Fluid Dynamics). Our simulation results showed good agreement with an experimental data. Concerning the quantitative prediction of silica deposition, we emphasize the importance of physical effects on silica scaling.