Conceptual Design of Column Dryer for Paddy Rice Including Fabrication and Testing of Prototype

Rice (Oryza sativa) is an important food crop which belongs to the Gramineae (grass) family. It is an excellent source of carbohydrates, vitamins (such as vitamin D), minerals (such as thiamine, iron, riboflavin and calcium), fibre and other nutrients that are valuable for human growth and health. As a staple food for more than 60 percent of the world population, rice is low in fat and salt and contains no cholesterol, preservatives or additives that are injurious to human health. Drying is one of the most important processes involved in the postharvest handling and processing of rice - other processes include threshing, parboiling, post-drying milling, cleaning, polishing and packaging. In this study, a column dryer was designed, built and tested for small scale drying of paddy rice in order to make the produce available all the year round in reasonable quantity, good quality and affordable costs. While designing and in material selection, consideration was given to portability, durability, ease of operation and maintenance, and techno-economic status of the and small scale rice farmers and processors who are the intended users of the dryer. The functional parts of the dryer included air vent, locking device, an 0.5 hp centrifugal fan inside a fan casing, thermostatically-controlled electric heaters inside a heating chamber and a drying chamber consisting the plenum chamber surrounded by two perforated grain columns. In operation, paddy is fed through the hopper and flow into the vertical grain columns surrounding the plenum unit in the drying chamber. Air is heated by the heaters in the heating chamber and the heated air is conveyed to the plenum chamber and passes through the grain-filled columns. Hence, drying takes place by heat and mass transfer processes in the two perforated vertical grain columns on either side of the plenum chamber while the residual air escapes through the vents on either side of the dryer. A preliminary test carried out on the dryer showed that it was able to reduce the moisture content of paddy rice samples from 22.36 % to 13.37 % indicating that the dryer performed satisfactorily. Powered by a 1.0 hp single-phase electric motor, the dryer has a production cost of USD 375 including labour and the cost of electric motor.