Design, development, and evaluation of rotary drum dryer for turmeric rhizomes (Curcuma longa L.)

Turmeric is a challenging crop to dry because of its heat sensitive volatile content and browning characteristics. In this study, a pilot scale biomass fired rotary drum dryer was developed for drying turmeric rhizomes. The drying experiments were conducted at 50, 60, and 70 degrees C air temperatures at an air velocity of 2 and 3 m/s and the drum speeds of 6 and 9 rpm. The turmeric rhizomes dried at a faster rate at the operating conditions of 70 degrees C air temperature, 3 m/s air velocity and 9 rpm drum rotational speed. Among the evaluated thin layer drying models, Page model comparatively gave higher R-2 values (0.998), lower sum of square error (0.001), and root mean square error (0.01) values. The effective moisture diffusivity of turmeric in the rotary dryer ranged from 0.33 to 0.5 x 10(-10) m(2) s(-1). The calculated activation energy of turmeric rhizomes was 19,338 kJ/kg mol(-1). The higher curcumin, oleoresin, starch, and color values such as lightness, redness, and yellowness value of 4.92%, 16.5%, 58.09%, and 59.87, 28.43, and 74.21, respectively, was observed at 50 degrees C, 9 rpm drum rotational speed and 3 m/s air velocity. The results indicated that the color of turmeric could be retained by drying at 50 degrees C. Practical Applications The present scenario, turmeric has been considered as an important crop against COVID-19 due to its antiviral properties and also food applications such as natural coloring agent and flavor enhancer. The unit operations involved in turmeric processing is washing, boiling, drying, polishing, and size reduction. The amount of curcumin content presents in turmeric decides its value. Drying is the time-consuming process compared to other unit operations and has an impact over the quality parameters of turmeric. Sun drying is the main traditional drying method normally practiced by the farmers for bulk drying of turmeric rhizomes. However, the sun-dried turmeric rhizomes lost its product value because of poor quality end product (dark yellowish brown color). This could be due to longer exposure of the product in sun causes change in the volatiles and color in turn degrades the market value and fetches lower price to the farmer. And also decreased drying rate, prolonged drying time, non-uniformity, and lesser energy consumption are the other factors that degrades further the quality of the product. Hence, a drying technology should be identified to overcome the problems faced by the farmers and also to dry the bulk capacities of the turmeric rhizomes at low cost. Rotary dryers are capable of processing larger capacities of various agricultural products having wide range of thermophysical and aerodynamic properties. The current research focused on developing a rotary dryer to reduce the drying time and also to retain the quality that benefits both farmers and industries by providing good quality product.