Production of green juice with an intensive thermo-mechanical fractionation process. Part I: Effects of processing conditions on the dewatering kinetics

The thermally assisted mechanical dewatering (TAMD) process is a new intensive solid/liquid separation device. When applied to ‘nature-wet’ biomass, the TAMD process significantly enhances the separation yield. The TAMD process couples in one stage a mechanical dewatering at low pressure (Papplied = 300 kPa in the present study) with a moderated heating (Twall ≤ 90 °C). An increment of pressure can be applied in a second stage to further enhance the dry solid content of the press cake. In the present study, the TAMD process was used to dewater spinach leaves and alfalfa stems and leaves. The influence of cutting, pulping and temperature on the fractionation kinetics and the extraction yield were specifically investigated. Experiments were carried out on a laboratory compression cell, heated through the piston. Results show that, at ambient temperature, pulping is an essential pre-processing unit operation to reach an extraction yield of 55%. Under moderate heating conditions (Twall = 50 or 70 °C), a thermally assisted mechanical dewatering, without any pre-processing stage, can remove 69% of the inherent water from alfalfa, that is to say an increase by 23% of the yield. But, compared with the conventional fractionation process, the duration of the mechanical fractionation must be at least twice longer. Beyond 70 °C, the temperature does not have any influence on the extraction kinetics. Cutting has a very limited influence with an enhancement of the dry solid content from 2 to 5% at best.