Abstract:
There is need to dry grain quickly and effectively after harvest and before storage to retain
maximum quality and to attain moisture content sufficiently low to minimise infestation by
insects, micro-organisms (bacteria, fungi etc) and to prevent germination. Drying systems require
substantial investment and to optimise their performance, efficient control systems are vital to
minimise energy usage. This study, involved cycling of exhaust air from drying trays to pre-dry
fresh grain. The drying temperatures used were 40 0 C and 60 0 C. Highest drying capacity of
3.17kg/hr occurred when pre-drying wheat with a moisture content of 21.657 % db, using a
drying temperature of 60 0 C. The lowest capacity of 0.54 kg/hr was recorded when no pre-drying
was carried at 40 0 C. The highest heat utilisation factor (HUF) of 87.6 % was obtained when pre-
drying 17.158 % (db) wheat at 40 0 C and the lowest (26.67 %) when no pre-drying was carried
on drying 21.657 % (db) wheat at 60 0 C. The highest drying efficiency of 72.29 % was obtained
when drying 21.657 % (db) wheat at 60 0 C and the lowest (22.44 %) when no pre-drying was
carried on 21.657 % (db) wheat at 60 0 C. Highest thermal efficiency of 33.86 % was obtained
when pre-drying 21.657 % (db) wheat at 60 0 C and the lowest (7.56 %) obtained when no pre-
drying was carried on drying 19.56 % (db) barley at 40 0 C. The average power consumed when
using a drying temperature of 40 0 C and 60 0 C was 1.25 kW and 1.775 kW respectively.
Good energy utilisation of pre-drying systems is supported by high HUF, overall thermal and
drying efficiency, which is more than double for conventional systems. By using low
temperature drying, the desired small thermal and moisture gradients can be achieved.
