CFD Simulation of a bubble column evaporator

Abstract

The combined principles of computational fluid dynamics (CFD) and heat and mass transfer are applied to design process equipment capable of performing both batch and continuous solvent swap operations at low temperature in the pharmaceutical industry. A bubble column evaporator was chosen a low temperature evaporator as it is a primitive, scalable and robust unit operation employed in a broad range of industries. A CFD analysis using OpenFOAM was subsequently performed on batch and continuous bubble column evaporators (BCE) for the methanol air system to provide data which experimental analysis cannot collect (with the same degree of detail) such as temperature distributions, concentration gradients and velocities across the column, which can then be used to predict methods of enhancing efficiency and evaporation rate. The effects of the gas flowrate, gas temperature and liquid flowrate on mass transfer in a BCE were investigated and the resulting system was analysed. Detailed analysis revealed that the gas was saturated almost instantaneously upon entering the column. It was concluded that both the gas flowrate and gas temperature are important factors affecting the rate of evaporation. An increased outlet gas temperature enhanced the rate of mass transfer in the system by up to 100% by increasing the gas phase saturation concentration of the solvent. This method proved particularly successful for the methanol-air system as the liquid had a significantly higher specific heat capacity than the gas and therefore the increased inlet gas temperatures had negligible effects on the liquid temperature.