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The Institute participated in the 18th Euro Fed LIPID Congress

Euro Fed Lipid gathers 11 scientific associations working on lipids, fats and oils. This federation aims to promote lipid science and technology as well as cooperation and exchange of ideas between scientists and technical experts on a European scale.

During its 18th congress, which took place from October 18 to 21 in a remote format, Patrick Carré, a process engineer at Terres Inovia, presented a lecture on "Renewal of theoretical approaches to mechanical extraction", highlighting a new approach to modeling seed pressing in order to improve the performance of industrial presses.

Extraction: a challenge for protein sovereignty

The issue of protein autonomy is more a question of concentration than of quantity of protein. France does not lack protein; it exports as much in the form of cereals as it imports in the form of soybean meal. What our animal feed industry needs, and more and more for human consumption, is an equivalent of soybean meal that is very rich in good quality proteins. To produce concentrated proteins from rapeseed or sunflower, it would be necessary to dehull these seeds, but the pressing of dehulled products remains particularly difficult. In the absence of hulls, the presses are no longer able to ensure satisfactory de-oiling without significant loss of capacity.
In addition, the preservation of protein qualities means that hexane extraction is no longer, or less and less, necessary. This reinforces the renewed interest in mechanical extraction (pressing). Many decentralized crushing units have appeared in recent years and continue to develop in the regions, these units also operate without the use of solvent. The technology of mechanical extraction is the subject of relatively little research, although there is significant potential for improving performance and the pressing of well-hulled products remains a challenge.

An observation on the technical difficulties of cold pressing

"Cold pressing of materials with high oil content and low fiber content such as sunflower kernels, cotton kernels, walnut kernels or jatropha kernels has long posed difficult problems for crushers. The observation is generally that of a blockage of the cake in the terminal part of the press and of a significant reflux of oil in the feeding zone", notes Patrick Carré.

However, published research on this issue has so far explained this difficulty mainly by a lack of friction due to the absence of fiber. "The fibers would be at the origin of a higher friction between the cake and the cage, preventing the solid matter from turning with the screw. Some authors have also suggested a relationship between the fibers and the viscosity of the cake" says this process expert.

A new technical approach tested by the Institute

What solutions can be found? "To try to renew these approaches, we propose to consider the issue from the angle of the plasticity of the cake, which allows us to understand the combined effects of water content, temperature, degree of cooking, shelling, geometry of the presses and their speed of rotation suggests Patrick Carré. According to this hypothesis, in fact, the pressing problem can be explained in terms of pressure generation in a continuous device where the axial thrust exerted by the screw needs the resistance opposed by the cake to generate pressure. This resistance is less a matter of friction and more a matter of the ability of the solid to deform under stress and flow toward the outlet. Plasticity is also related to the compressibility of oil-bearing materials."

This approach proved very useful in recent work to improve the performance of a small pure sunflower kernel press. "After modifying the screw, widening the bar spacing, we were able to adjust the plasticity of the meal by modulating its water content and temperature. We thus went from being unable to press (hard plug and oil reflux to the feed zone) to producing cake with less than 10% oil".

This work has highlighted the effect of slippage of the cake, which results in an irregular output of the press, the axial speed varying greatly depending on the rotation of the screw.