Scale formation in desalination plants: effect of carbon dioxide solubility

Modeling of the release of CO2 in the multi-stage flash distillers requires knowledge of the CO2 solubility in seawater at the conditions prevailing in the system. The evidence from literature is that measurement of the solubility of CO2 in pure water has been extensively studied, whereas that in saline solutions has not. Several studies have investigated the solubility of CO2 in seawater under different temperatures and pressures, but they have not covered the conditions that prevailed in the desalination plants, such as low pressures and high temperatures. In the low-pressure regime (i.e., near atmospheric pressure), the gas solubility can be theoretically estimated by considering the ionic strength and the salting-out parameter. Gas solubility measurements can be made as a function of the seawater temperature and salinity. Fouling in the MSF plants occurs as a result of alkaline scale formation and it is known that the rate of formation of calcium carbonate and magnesium hydroxide in seawater depends on temperature, pH, concentration of bicarbonate ions, rate of CO2 release, concentration of Ca2+ and Mg2+ ions, and total dissolved solids. This review presents an overview of the CO2 solubility in the brine, carbonate equilibria in the seawater and the various correlations used to characterize the CO2-seawater system. Also, some gas solubility equipment has been mentioned.