Bucher Unipektin AG is a traditional and leading manufacturer of individual machines and complete systems for the beverage and food industry. In the course of a research project, a novel desublimation system for continuous and discontinuous freeze drying processes is to be developed.
In the freeze drying of foodstuffs, the energy demand is about twice as high as in standard pressure convection drying. The energy efficiency of this process, based on the pure sublimation enthalpy of 0.8 kWh/kgH2O of the water to be removed, is about 10%, depending on the size of the system. The sublimation of the frozen water in the drying chamber and the subsequent desublimation of the water vapour in the desublimation system account for the largest share of the energy demand, approx. 40-70% depending on the operating pressure. In the production and operation of freeze drying systems, the desublimation system accounts for about 30% of the total costs. The desublimation system thus has a decisive influence on the energy and economic parameters of the entire freeze-drying process.
The aim of this Innosuisse funded project is to develop a desublimator prototype that stands out from the current standard due to its modularity, standardised design and high energy efficiency. To begin with, a reference process of an existing, quasi-continuously operated small-scale plant at Bucher Unipektin AG will be investigated theoretically and experimentally. A mathematical-physical model of the desublimation process, which represents the dynamic heat and mass transport in a temporally and spatially discretised manner, is being developed for this purpose and validated with the reference system. This will be used to simulate the newly conceived regeneration concepts of the desublimator. Critical sub-processes are investigated experimentally in the large-scale laboratory of the HSLU with functional models, with the findings flowing back into the simulation models. With the help of the simulation results, a desublimator prototype of the more promising concept will then be designed, manufactured and experimentally evaluated at Bucher Unipektin AG. After further optimisation steps, recommendations for upscaling and series production of the new desublimator for large industrial plants will be derived.