Characterization of oilseeds mechanical expression in an instrumented pilot screw press

Abstract

This work studies oil seeds mechanical expression in a screw press. For this purpose, a pilot-scale screw press (0–40 kg/h) was instrumented by installing sixteen pressure sensors and three temperature probes throughout the screw. Canola (Brassica napus L) and flax (Linum usitatissimum) seeds were used for investigation. The impact of the screw rotation speed on the press performances and the matter flow inside the press was investigated. The screw press capacity, passage time, extraction yield and specific energy consumption were studied is the range of 0–18.2 rpm. For each experiment the radial pressure, the internal residual oil content and the matter velocity evolution were measured all along the screw.Results show that increasing the rotation speed enhances the press capacity and decreases the passage time, reduces the extraction yield and the specific energy consumption. The recorded data allowed the identification of different functional sections of the screw press (feed, compression and mixing/relaxation sections) in relation with the screw geometry. In the compression sections, high pressure leads to oil expression and the formation of hard cake. In the mixing sections, pressure falls to zero and press-cake becomes friable. The matter velocity in the mixing sections is quick as compared to that in compression sections. Furthermore, results show the existence of oil reflux phenomena inside the screw press cage.Based on the obtained results, the continuous screw press behavior was schematized as a succession of several individual batch presses with intermediates steps of press-cake mixing and oil refluxes in order to facilitate process modeling.