3) The art of Dehydration

The high energy cost of drying processes forms a strong incentive to search for alternative technologies that consume significantly less energy. This session focusses on two such alternative technologies to remove water or recover compounds form aqueous streams: Super Critical CO2 and Eutectic Freeze Crystallization (EFC). Topics will be discussed in the context of both application and fundamental principles.


Maarten Schutyser, Wageningen University & Research:
Throughout the last decades many drying technologies have been developed, often connected to specific applications and following trial-and-error approaches. Due to the complexity of the drying processes, food industries make often conservative choices, for example to increase their capacities with long-existing, traditional drying technology. Given the urgent need to increase the sustainability of our food production, there is an increasing interest to invest into research on drying technology to make a step change with respect to technology choices. The focus of my research is to gain understanding of the complex phenomena that occur at multiple length scales during drying of foods, and identify those that are important in determining process efficiency and product quality. This understanding is translated into the optimization of existing and design of new drying strategies that are more efficient and add desired functionality. My research is in line with the mission of the Netherlands Working Group on Drying (NWGD), which is to stimulate development and application of innovative sustainable drying technologies that provide better product quality.

Ruben Halfwerk, Wetsus & Wageningen University:

Eutectic freeze crystallization (EFC) is a newly developed crystallization technique that operates at subzero temperatures. The eutectic point of an aqueous solution is the concentration and temperature were both the solvent as the solute starts to crystalize simultaneously. Due to the density difference between the solvent and solute, separation by gravity is possible. A pure stream of ice and solute can then be extracted, the remaining liquid can be separated further or recycled again into the process. In comparison with other separation technologies like evaporation, EFC has a low energy requirement and has the ability of complete conversion of feed in to water and solidified solutes. Previous research has been focused on separating salts from brines emitted from RO plants. However it is also possible to separate organic substances. This research focusses on the recovery of heat sensitive products and concentrates in the agro and food industry. An EFC setup has been developed by Coolseperations bv. and Wetsus. The first part of this research will look at the recovery of lactose from delactosed whey permeate (DLP), which is a byproduct created by removing lactose from whey. In this project, parameters of interest are crystal growth, ice and solvent quality with respect to size, shape and purity and the influence of impurities on the crystallization behavior.

Shin Yee Wong, Singapore Institute of Technology:
In the dairy industry, lactose crystallization during refining typically generates large number of fines (< 100 µm), which greatly reduces the efficiency of downstream processes, resulting in low recovery. Theoretically, the crystal size distributions of the lactose crystals can be controlled by two major kinetic steps: nucleation and growth. Nucleation is strongly related to the metastable zone width (MSZW), defined as the area between the saturation curve and labile zone. Inside the MSZW, crystal growth is fastest with least secondary nucleation. However, existing data published in the 1920s were not suitable for directing an industrial operation. In this talk, refined metastable limit (ML) will be presented. Then, the talk will focus on applying the newly established reference graph (ML) together with Computational Fluid Dynamics (CFD) to analyze and design a crystallization operation. From all these studies, it was demonstrated that depending on the crystallizer design, large lactose crystals with minimal fines can be produced when operating in the optimal region in the MSZW. Finally, the technology was transferred to the dairy industry where it was successfully tested.

Gerard Hofland, FeyeCon:
Drying using CO2 as a drying agent has been investigated at pilot scale as an alternative to energy intensive drying processes for fruits and vegetables as well as powders. CO2 drying is operated at elevated pressures but close to ambient temperatures in absence of oxygen. Maintaining product quality and reducing energy cost are the main drivers for introducing such processes.
Product quality and microbial safety aspect have been investigated at different scale levels. Drying was performed on vegetables such as bell pepper and beetroot, as well as herbs such as parsley and coriander. Scaling factors were analysed on the basis of the level of dryness and product quality parameters such as colour, shape and shrinkage also with respect to shelve life. Subsequently, energy costs and options to save water were evaluated. Finally, steps towards industrial production have been demonstrated.



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