DRYING OF RESIDUAL GRAINS OF ANNATTO IN A HEAT ACCUMULATOR DRYER COMBINED WITH DRYING IN A SOLAR DRYER

Abstract

This paper is a study of the drying process of residual grains of
annatto in a heat accumulator dryer during the night combined
with a solar dryer during the day. Different mathematical models
were adjusted regarding experimental data for the dryings and
for determining the effective diffusivity for all the processes. The
grains were divided into two groups; one with oil, reproducing the
conditions of the grains after the oily extraction of bixin, and another
group without oil. The drying of the annatto grains of during the night
was performed with a heat accumulator dryer, which consisted of
solar panel systems that heat water, which is transferred to a thermal
tank where it is used as a heat source; during the day a solar dryer
was used. Residual grains of annatto with an initial moisture at
~18 % w.b. were dehydrated until they reached ~5 % w.b. Combined
drying using a heat accumulator dryer and a solar dryer proved to
be effi cient, with samples presenting lower amounts of moisture
compared to the control samples. Midilli’s equation was considered
the best model to represent the kinetics of drying residual grains of
annatto both with and without oil. Grain samples presented effective
diffusivity in the order of 10-9 m2 s-1.