Abstract
The aim of this work was to investigate the energy efficiency of infrared radiation drying (labeled IR) and hot air drying (labeled HA) of spirulina assisted by capillary drainage (labeled DC). Capillary drainage effect was introduced by a porous material (filter paper) placed under a thin layer of spirulina biomass of 3mm thickness. Infrared drying experiments were performed using a laboratory IR-30 moisture analyzer while convective drying experiments were realized in a pilot-scale drying tunnel. The spirulina was dried at two initial moisture contents on dry basis; 5kg/kg and 7kg/kg. For both infrared and convective processes, the drying temperature range was 50 to 80 degrees C and the air velocity was 0.5m/s. The air humidity was not controlled but calculated for each temperature from the dry and wet bulb temperatures. The drying kinetic coefficients were identified by fitting the falling rate drying period data by Lewis semi-empirical model. According to our results, the capillary drainage provided a real possibility to dry faster and thus reduces the energy consumption for both infrared and convective drying processes. The time reduction percentage, averaged over the range of the operating conditions, was around 60% for infrared drying and 40% for convective drying. Moreover, the mean maximum drying rate was much higher for IR-DC drying (2.091.10(-3)kg/kgs(-1)) than HA-DC drying (1.115.10(-3)kg/kg.s(-1)). As concerns, the kinetic drying coefficient, this parameter was significantly increased by the presence of the porous material essentially for infrared drying.