Thermal analysis of hot air drying of chicken manure pellets in a modified portable horizontal rotary dryer

This study aimed to investigate the heat and mass transfer occurring during the drying process of chicken manure pellets in a modified portable horizontal rotary dryer, where hot air was employed as a heat source. The modified rotary dryer consisted of a drying pipe (1 m × 0.3 m i.d., thickness 3 mm) responsible for heat exchange and a 1/2-hp electric motor installed for power transmission through the pipe. Chicken manure pellets with an average diameter of 3–5 mm were utilized for the drying process with a feeding rate set at 10 kg/h. In the experiment, the hot air flow rate was kept constant at 0.25 kg/min with the inclination angle of the pipe set at 1º, drying temperatures at 30–85 ºC, and rotation speeds at 10–20 rpm. The results showed that the optimal drying condition was achieved at a temperature range of 70–85 ºC and the rotation speed at 10 rpm, which resulted in the heat load of 4.2 kW in the system corresponding to the heat of 2.87 kW used for the drying process. The drying rate was obtained at 4.85 kg water /h and thermal efficiency at 68.43%, which could reduce the moisture of the manure pellets from 50%db to 18.55%db within 30–40 min. As with multiple regression analysis, there was a significant correlation between drying rate and manure moisture, moisture ratio, drying heat, and thermal efficiency, with the R 2 values of 0.95, 0.97, 0.98, 0.95, and 0.94, respectively.