Intensification of the convective drying process of Arthrospira (Spirulina) platensis by capillary draining: effect of the draining support

Abstract

The aim of this work is to study the intensification of the convective drying process of Arthrospira (Spirulina) by capillary drainage. Capillary drainage effect was performed by the integration of different draining supports, namely cotton, microfibers, 30 μm fabric, and 80 μm fabric, between the biomass and the drying tray. Drying tests were carried out in a pilot-scale drying tunnel at a free-stream temperature between 39 and 42 °C, at air velocity of 0.5 m s−1 and at air relative humidity around 20%. The Arthrospira biomass was set at two different initial moisture contents on dry basis: 7 kg kg−1 and 5 kg kg−1. For each of these initial moisture contents, the fresh paste was spread over the different draining support, either in a thin layer (dimensions 80 × 80 × 3 mm3) or in cylindrical extrudates (3-mm diameter and 120-mm length) with two different spacings (10 and 20 mm). Drying experiments of biomass in thin layer after the integration of the different draining supports, particularly the 80-μm mesh fabric, lead to a significant drying time reduction compared to that performed without any draining support. For this most effective support, the percentage time reduction was around 30%. However, the percentage time reduction was around 35% for drying tests of biomass in cylindrical extrusions using 80 μm mesh fabric as a draining medium. For all drying tests, the drying kinetic coefficient kx was identified by fitting the falling rate drying period data by a first-order kinetic equation (Lewis model). This coefficient was significantly increased by the presence of the porous material. Its value was equal to 5.604 × 10−4 g dry matter s−1 for drying test without any support and reached a value of 11.556 × 10−4 g dry matter s−1 for drying test with 80-μm mesh fabric.