The release of CO2 in multiple-effect distillers has scarcely been investigated and little has been published about it. There is no approach available to reliably predict the release rates in individual stages and the effects of influencing parameters. Until now the dimensioning of the design venting rates has been based mainly on experience and very sparse experimental data. The present work was aimed at gaining an in-depth understanding of the physical and chemical processes involved in CO2 release and the carbonate system in multiple-effect distillers. A model has been developed that describes the CO2 release and the carbonate system in multiple-effect distillers. Included is the flow path of brine through the final condenser and the evaporator stages. The desorption of CO2 was described as a problem of coupled mass transfer with chemical reaction. The mass transfer coefficient and the phase interface area were studied for the fluid dynamics of failing water films on horizontal tubes.