Scaling of calcium carbonate (CaCO3) in pipes: Effect of flow rates and tartaric acid as additives on induction time and phase transformation

Abstract

Calcium carbonate scale usually precipitates and grows on industrial equipment such as piping system, causing blockages in the pipes, thus reducing mass and heat transfer. This paper presents experimental results of calcium carbonate scale formation in a piping system. The scale-forming solution was prepared by mixing equimolar solutions of CaCl 2 and Na2CO3, with a concentration of 4,000 ppm of Ca 2+. The solution flow in a pipe with a laminar mode at: 25, 35,and 45 mL/min. Other parameters selected in this experiment were the addition of additive: tartaric acid (C4H6O6) concentrations of 4 ppm, 6 ppm and 10 ppm. The process of the scale growth was observed by measuring the conductivity of the solution coming out of the test pipe. The scale formed was characterized using SEM for morphology and XRD for crystalline phases. It was found that in all experiments, the conductivity decreased abruptly after certain induction period. The induction period varied from 4 to 12 min, which means that the scale began forming after 4 to 12 min after mixing the solution. Higher flow rates produced more scale mass indicating that the increasing flow rates promote scale formation. SEM analysis showed that the scale was a mixture of rhombohedral and irregular spheres, while the crystalinity of the scale was found to be mostly calcite as shown by the XRD.