Batch Drying Kinetics of Cardamom in a Two-Dimensional Spouted Bed

Abstract

Cardamom (Elettaria cardamom L.) is considered the “Queen of the Spices” and enjoys a unique position in the international spices market. It finds application in culinary art for flavoring of foods, pharmaceutical, perfumery, cosmetics, and several other industries. Cardamom capsules contain 80% (wb) moisture content at the time of harvest, which must be brought down to 8–12% (wb) for safe storage. Drying is one of the most important unit operations in the commercial production of cardamom, because it determines the color of the end product. Conventionally, the cardamom capsules are dried in a kiln dryer, which yields a poor quality end product. The batch drying kinetics of cardamom were investigated experimentally in a two-dimensional spouted bed using both continuous and intermittent (on/off) spouting and heating schemes. The parameters investigated include inlet air temperature, bed height, slant angle, separation distance, draft tube height, and intermittency of spouting. The results indicated that the drying kinetics were comparable with fluidized beds for slow drying materials, where the drying rate is controlled by internal moisture diffusion. The drying characteristics of the cardamom in the spouted bed indicated that the inlet air temperature was the parameter that most significantly affected the drying rate as well as the quality of the product. It also showed that the intermittent drying of particles took 13 to 18 h compared to continuous drying, which ranged from 9½ to 13 h. Intermittent drying can save up to 25% of the thermal energy, in addition to yielding a better quality product in terms of color, flavor, and percentage yield of oleoresin extract.