Factors influencing CaCO₃ scale precipitation and CO₂-H₂O system in flowing water in natural water piping system

Abstract

This work considers the factors influencing CaCO₃ scale precipitation and CO₂-H₂O system for flowing water in steel pipes. An experimental setup is used to simulate the pumping system of water supply in natural water piping system in which a certain amount of water is pumped at a certain pH, temperature, and flow rate as initial conditions. The pH values, temperatures and flow rates increase with the time of circulation of 5 h of each run. The pH of the water samples ranged from 7.2 to 8.0 and temperatures increase by 18–20°C when the flow rates change from 43.3 to 58.3 L/min, respectively. Water samples investigated in this study exhibit high concentration of Cl-, SO4 ^2- ₄ and HCO^- ₃ – as the major anions and Ca²⁺ as the major cation. Saturation ratio of calcite (Ω_calcite) increases from 0.03 to 0.10 units, consequently, the amount of scale precipitation increases from 0.2 to 0.4 mg CaCO₃/kg of feed water. The concentrations of HCO^- ₃ and CO^2- ₃ decrease from initial to final conditions, while the concentration of CO₂ increases. The saturation with respect to CO₂ was found to be very low and decreases with increasing flow rate and temperature, this implies that CO₂ is released from the water, leading to an increase in the pH value and thereby increasing the possibility for CaCO₃ to precipitate.

Keywords:

• CaCO₃ precipitation
• Natural water
• Piping system
• Flow rate