Simulation of CO2 release 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 seawater through the final condenser and the evaporator stages. The desorption of CO2 was described as a problem of coupled mass transfer with chemical reaction. A computer program was written for simulating the CO2 release and the carbonate system. The CO2 release rates as well as the HCO3-, CO32-, CO2, H+ and OH- concentrations in the brine were simulated for a multiple-effect distiller with typical dimensions at various operating conditions. The effects of top brine temperature, concentration factor, seawater salinity and pH on CO2 release and the carbonate system were studied. The release rates of CO2 decrease from the first to the last stage. CO2 release increases with increasing top brine temperature. The total CO2 release (sum of the CO2 release in the stages) increases from about 14g CO2 per ton of feed water at a top brine temperature of 60degreesC to about 18.2 g/t at 70degreesC. Between 14% and 18% of the total inorganic carbon content in the feed water is released as CO2.CO2 release rates increase with decreasing concentration factor. Relating the desorption rates to the feed water flow rates, the specific CO2 release increases with the concentration factor. CO2 release rises with increasing salinity and decreasing pH of the seawater.