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Table 6 Schematic overview of different scale and ripple formation mechanisms in the ground-level pipes between filter and heat exchanger with indication of the calculated scenarios 1–4. No calculation scenarios were defined for transition phases (start of pump, shut down of pump) since these could be ruled out for several reasons

From: Rippled scales in a geothermal facility in the Bavarian Molasse Basin: a key to understand the calcite scaling process

  Flow rate, L/s Flow velocity, m/s Pressure, bar Process
Start of production 110 1.40 12 Remobilization of existing scale particles due to turbulence. Pump rate is increased too fast to allow for ripple formation and stabilization
Full production (scenarios 1 and 2) 110 1.40 12 Slow scale precipitation due to degassing and oversaturation. Velocity > calculated ripple washout velocity, therefore no ripples predicted
Shut-down of production 0.1 - 0.5 0.00 1 - 4 Solid particle deposition (ripples) of suspended particles followed by stabilization of scales due to sudden pressure drop and degassing. Too little particle supply
Acid treatment (scenarios 3 and 4) 5 0.06 1.8 - 2.6 Acid causes remobilization of partially dissolved scale particles and subsequent solid particle deposition (ripples). Oil prevents total dissolution of scales. Stabilization of ripples takes place when pH rises too high
Flushing of facilities with tap water after acid treatment (scenarios 3 and 4) 6.5 0.08 1.6 - 3.5 Stabilization of ripples by calcite precipitation due to high calcium ion concentration in the cleaning solution and a neutral pH of the tap water