Trond Andresen

Atmospheric Freeze Drying—Modeling and Simulation of a Tunnel Dryer

Drying is an important unit operation in processing of foods and other biotechnological products. Vacuum freeze drying is said to be the best drying technology regarding product quality of the end product, but the disadvantages are, among others, expensive operational costs and batch drying. Atmospheric freeze drying was introduced to lower the production costs of high-quality dried foods, and the need of simulation tools became important in estimations of the industrial drying processes. A simplified mathematical model (AFDsim) is developed based on uniformly retreating ice front (URIF) considerations. The model is used to calculate theoretical drying curves of atmospheric freeze dried foods in a tunnel dryer. Studies of thermal and mass transfer properties during drying are essential for understanding the changes in product quality and for designing and dimensioning the drying process. The model can be used to simulate industrial atmospheric freeze drying of different foodstuff in a tunnel. The results from AFDsim modeling are in good accordance with the experimental results.

Enabling Efficient Heat Recovery from Aluminium Pot Gas

In the present work, previous studies carried out by the Norwegian aluminium industry and research centres with the aim of recovering heat from aluminium production off-gas, are reviewed. The main challenge in improving heat recovery is the fouling phenomena, which is due to the presence of particulate matter and corrosive gases in the off-gas. Fouling can occur due to particle deposition, condensation of corrosive acids and scaling reactions, which in turn can build up hard layers, particularly, on heat exchanger surfaces. The review focuses primarily on fundamental studies (theoretical and experimental), which address off-gas composition characterization, particle size distribution and particle deposition phenomena in laboratory and industrial environments. Moreover, it presents commercial concepts already implemented in industry applications. Upcoming activities in regards to the scaling phenomena, which include the design of a cold-finger for laboratory and industrial measurements, as well as mathematical modelling using CFD, are also discussed.