Development and validation of a heated drying air diffusion system to optimize rotary dryers and final coffee quality

The final quality of pre-processed coffees is influenced by the applied drying technology. Thus, the aim of the study was to develop and validate a heated air flow diffusion system to optimize and reduce the drying time of rotary dryers and improve the final quality of coffee. Computational fluid dynamics was used for the simulation of the air fluid dynamics in the combustion chamber of the heat generator. It was observed that the energy losses in the upper and lower walls of the heat generator chamber were higher with an increase in the convective heat transfer coefficient. It was found that the rate of fluid flow presented a fully developed profile, in which the higher speed value was found in the central region of the outlet. The reduction in moisture content during coffee drying was directly proportional to the increase in temperature. The Midilli model shows the best fit to describe the drying curves of the coffee. The effective diffusion coefficient increases with increasing temperature of the drying air. It was observed that the adjustments of the fluid dynamics in the burning of gas and the adaptation of the diffuser system significantly influenced the drying time and final quality of naturally processed and pulped coffees. In conclusion, the adapted technological set, a rotary dryer with gas heating and diffusion of heated air, had a high performance in the final quality of the coffee, and for this reason it is recommended to producers and the industry.