The Effect of Supersaturation and Additives on Calcium Carbonate Scaling at Mono Ethylene Glycol Pre-Treatment Conditions

Abstract

In this report the effect of supersaturation and additives on calcium carbonate scaling under mono ethylene glycol (MEG) pre-treatment conditions (T=80°C and 50 wt% MEG) have been studied. The additives used are magnesium and ferrous, both separately and together at various concentrations of magnesium. The effect of magnesium was also studied at 80°C in pure water and at 25°C in the presence and absence of MEG. Both quantitative (amount of scale) and qualitative (morphology) studies of the scaling were conducted. The morphology and polymorphism of the precipitates were studied using SEM and XRD. The supersaturation ratio in the reactor at steady-state was found to increase with increasing concentration of magnesium in the feed. In the presence of magnesium, the amount scaling on the reactor wall was increased. Aragonite was the only polymorph found in the presence of magnesium and the aragonite morphology progressed from branched aragonite to dumbbells and polycrystalline spherulites with increasing magnesium concentration. The presence of ferrous was found to decrease the supersaturation in the reactor at steady-state and the amount of scaling on the reactor wall, both in the absence and presence of magnesium. However, the amount of scaling increased with increasing feed concentration of magnesium. The presence of ferrous seemed to favor calcium and magnesium consumption by the bulk particles over consumption by the scale. Polymorphs formed in the presence of only ferrous and both ferrous and magnesium were aragonite and calcite. Oxidized ferrous was found to decrease the scaled amount even more than ferrous. The resulting particles size on the scale on the glass was found to be smaller in the experiments with oxidized ferrous compared with the experiments where no oxidation was observed. The two experiments conducted in the absence of MEG with magnesium, one at 80°C and one at 25°C, resulted in a scaled amount more than five times larger than when MEG was present. In the presence of MEG, the amount of scale was smaller at 25°C than at 80°C at the otherwise same conditions.