Spirulina is a cyanobacteria filled with therapeutic and nutritive properties that can be easily digested. It contains 71% protein by weight and a higher percentage of GLA (Gamma-Linolenic Acid) than any other plant. GLA has contributing properties of reducing blood pressure and blood cholesterol. After harvesting, the Spirulina is drained, sun-dried and dried in a convective oven. During the prolonged rainy season in Southern Thailand, convective drying alone can be very slow and energy consuming. Thus, this research investigated the effect of air-impingement technique on thin-layer drying of Spirulina. First, the effects of temperature (40, 50, and 60°C) and film thickness (2 and 4 mm) on the drying rate were obtained using a lab-scale dryer with a product capacity of 600 g. For an air velocity of 1 m/s, an increase in temperature up to 60°C resulted in an increase of the drying rate, while increasing the film thickness to 4 mm increased the drying time by 50%. In the second part of the study, a pilot-scale impingement dryer (1.2 m x 1.2 m x 1 m) was designed and constructed. The dryer consisted of 3 levels and can handle up 2.8 kg of fresh Spirulina per batch when arranged in a 2 mm layer film. The temperature distribution inside the dryer and the effect of air velocity (1.3 and 2.6 m/s) on the drying rate were investigated. From thermocouple measurements, the temperature deviation was less than 10% from top level to bottom level when compared to the average value. Moreover, using the specific moisture evaporation rate as the performance indicator, it was found that an air velocity of 2.6 m/s was more efficient than one of 1.3 m/s.
