Robust design of flash evaporators for must concentration applications in wine production

In recent years, flash evaporation processes have received an increased attention in the wine industry for must concentration applications. Specific constraints related to the wine industry area had lead to many improvements of flash evaporators initially designed for seawater desalination. In particular the quality of the vintage, the transportability of the system and the environmental impact are of main interest. Moreover, the preliminary design of such systems must also consider robustness criteria. Obviously, variations of temperatures and flow rates of liquids at the inlet of the process can dramatically impact the quality of the product at the system outlet. In particular, deviations from the target values of temperature and alcoholic volume fraction can lead to a severe degradation of the vintage. As it is common in product design to have multiple performance measures, the robust design problem is addressed using a multi-objective approach. A trade-offs is introduced between two main design objectives: (i) the improvement in overall performance (product quality, transportability, environmental impact and costs) and (ii) the lowering of the sensitivity of the product quality under uncertainty. These main objectives are related to several elementary objectives corresponding to design criteria and a preference aggregation method is used to formulate the two different design objectives. Objectives are linked to weighting parameters values equivalent to priority levels. The selection of the most preferred design solution is discussed according to different trade-off strategies. The generation of the Pareto set is addressed by the non dominated sorting genetic algorithm NGSAII. From computing results, our recommendations concern the compromise between performance and robustness of flash evaporators. In this context, the final alcoholic volume fraction of the wine is the most sensitive parameter, which justify to maintain a high value of evaporative capacity when designing this type of system.