Effect of anti-scale agents on the solubility of CO2 in seawater at temperatures of 60 to 90ºC and pressures of 1–2 bar

The objective of this work is to present experimental data that would show the effect of temperature, salinity, pressure and the presence of anti-scale additives on CO2 solubility in seawater. The paper examines the solubility of CO2 in real seawater and real seawater dosed with two different anti-scale additives. The study has been performed at temperatures between 60ºC and 90ºC and at pressures of 1 and 2 bar. To assess the effect of each anti-scale additive on CO2 gas solubility varying doses, 2–10 ppm of anti-scale additive have been used. For the purpose of the experimentation an experimental rig has been designed to ensure adequate contact between the gas phase and the aqueous phase. The continuous quantitative analysis of CO2 concentration flowing from the experimental rig was measured using a CM-5011 Carbon Coulometer. A mass balance was carried out to calculate the amount of CO2 absorbed into solution; Henry’s law constant was then calculated.

Acknowledgment As the temperature of the system increases, CO2 solubility in aqueous solutions usually decreases. The laboratory investigations showed that adding an anti-scale agent increased the CO2 solubility in the seawater. The CO2 solubility also increases as the concentration of the anti-scale agent in the system increases. A higher CO2 concentration in the seawater at high temperature would in principle retard scaling and is therefore advantageous. The anti-scale additives vary in performance depending on the type of mechanisms by which they function in controlling or retarding scale formation. The absorbance of CO2 in seawater is a function on the anti-scale additive used. When Genesys SW anti-scale additive was added to the seawater, CO2 concentration in the seawater increased and the increase was more evident at 60EC and 80EC than at 90EC. The Sokalan MSF type anti-scale additive absorbs more CO2 in the seawater at 90EC than when the Genesys SW anti-scale additive was used. The relative drop in CO2 solubility at 90EC for each anti-scale additive investigated demonstrates that the thermal stability issues of anti-scale additives need consideration. The nature and effect of scale precipitation after pressure release in the flash chamber is very important, and a sudden loss of CO2 from bulk brine and then corrosion especially in the presence of other non-condensable gases will occur.