MODIFIED COFFEE DRYING SYSTEM

The Bakker Arkema model for grain drying in deep bed was modified to simulate the process of coffee drying in deep beds using the heat and mass transfer model for thin layers proposed by Sokhansanj and Bruce (1987) and adapted for parchment coffee by Abud (1998). A prototype of the drying bin was built and tested in the Agricultural Experimental Station in Adjuntas, Puerto Rico. This unit was used for validation of the mathematical model. The model predicts with a maximum deviation of 3% (wb) the moisture level of the bean throughout the drying process. The airflow direction was reversed in the prototype every six-hour intervals and air temperature was set at 55°C. Twentyseven hours was needed to reach a moisture level of 11 w.b in the prototype using a flow rate of 50 cfim per square feet. A Comparison between experimental and theoretical values show a maximum deviation of 3% w.b