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 (&OHgr;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 CO2-3 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.