Solutions Concentration through Multistage Membrane Process with permeate recycle: Modeling & Simulation

Many process industries at some point needs to concentrate liquid solutions. Most of the time solutions are aqueous. The conventional method used to concentrate aqueous solutions is evaporation, which is not only very energy intensive because of high latent heat of water vaporization but also results in the degradation of the heat sensitive solutions. Membrane technology has the advantage to concentrate the liquid solutions without phase change and therefore, needs very less energy compared to the evaporation. The challenge in membrane concentration is its upper limits, because the evaporation is capable to concentrate the solutions up to 70 to 80% while the concentration driven membrane processes can concentrate up to 65 to 70% but they have very low permeate fluxes and needs a third component as solvent, the recovery/disposal of the which is also problematic. Pressure driven membrane process can concentrate up 25-30% economically due to osmotic pressure limitations. Multistage Pressure driven membrane processes with permeate recycle can concentrate the liquid solutions to much higher levels up to around 50 % compared to single stage pressure driven membrane processes without the needs of any solvent. This process has sown a significant energy savings. The multistage membrane concentration
processes, as shown in figure1, used the combinations of high and low rejection membrane in different stages. The selection of appropriate membrane for each stage is the key factor in the design of the multistage membrane concentration processes. In the present work a simulation and optimization strategy has been developed for a 3-stage concentration process as shown in figure1. The optimization approach is able to select not only the appropriate membrane for each stage but is also cable of predicting the appropriate number of stages for specific concentration ranges or levels. The simulation algorithm is shown in figure2. A case study of clarified sugar juice concentration from initial concentration of 15 % to final concentration of 50 % will be presented in the conference in which modeling, simulation and optimization approach will be discussed. Furthermore, the net energy savings compared to the multi-effect evaporation processes will also be presented.