Experimental investigation of the solar drying of Tunisian phosphate under different conditions

This paper presents a comparative study on the solar drying of Tunisian phosphate in the open sun, under greenhouse and by a parabolic dish concentrator. The phosphate drying kinetics using the three experimental devices were investigated. The behavior of the moisture content during the drying period was discussed. The maximum phosphate temperatures reached near midday, in open sun, under greenhouse, and at the focus of the parabolic dish concentrator were respectively 50 °C, 59 °C and 102 °C, while the residual phosphate moistures were respectively 0.042, 0.022 and 0.006 as kg water/kg dry matter. Drying phosphate by these three solar processes reached the marketing standards, of a residual water content ranging between 0.02 and 0.04 kg water/kg dry matter, after 05 h 20 min. In addition, nine thin-layer drying models were fitted to the experimental data to select a suitable drying equation. The Midilli model was found to best describe the drying behavior of phosphate using the three solar processes. This work shows that the drying by the parabolic dish concentrator gives results whose perspectives are satisfactory compared with the drying in the open sun or under greenhouses.