Experimental study of the drying of Pergamino coffee using microwaves and fluidization

REYES CHAPARRO, JOSE; ARBALLO J.R; CAMPAÑONE, L.A.

Congreso; 11th World Congress of Chemical Engineering; 2023

The objective of the present work was to study the drying kinetics and temperature increase of coffee in a fluidized bed combined with microwaves, analyzing the influence of microwave power, temperature and forced air velocity on the processing time. The experiments were carried out in a laboratory equipment which consists of four main components: microwave cavity, drying chamber, piping and centrifugal blower. The microwave cavity is equipped with a magnetron with nominal power of 700 W and 2450 MHz frequency (MPD8620N, Philco, Argentina) in which the fluidized bed system was installed. The air velocities were supplied by the centrifugal blower with 15000 rpm (Black and Decker, Argentina), which was controlled by means of the frequency inverter (El toroide®, Argentina). A hot wire anemometer was used to measure the speed and temperature of the inlet air. The moisture content and surface temperature of the samples were recorded at 5-minute time intervals during the drying process. The process was carried out until the grains reached the final moisture level between 10 and 12% w.b. The experimental design corresponds to 3 levels of microwave power (0, 30 and 50%) and different air velocities (0, 1.7 and 3.4 m/s) at 25 ºC and 40ºC. All measurements were performed in triplicate. Drying curves and the corresponding thermal images were obtained from the experiments for each operating condition. The experimental curves showed that the drying rate increases with air velocity and microwave power. The best operating condition for the combination of microwave and fluidized bed with respect to process time was the use of an air velocity of 3.4 m/s with 50% microwave power in 105 min at a final moisture content of 11.8% w.b.