How to use the DRYIT semi-continuous tray dryer
Practical Action
= Time to dry material on bottom tray (minutes) / Number of trays in dryer
For example: 180 / 15 = 12 minutes
In reality the interval should be less because material starts to dry almost as soon as it is
loaded into the Dryer.
Each time a tray is removed from the bottom of the stack a tray of fresh material should be
loaded at the top.
It is possible to continually unload and load the Dryer provided the amount of prepared raw
material is available.
To calculate potential total amount of raw material that can be dried in 8 hours
Tray change time = 12 minutes
Kg per Tray = 3kg
Initial change time = 3 hours
Hence, after 3 hours, 3 kg processed. After 3hrs 12 mins, 6kg processed etc. Start drying at
9am, after preparing raw material since 7.30am At 12 pm 3kg. Every hour = (60/12)x3 =
15kg
Finish drying at 4pm. Therefore total fresh material processed per day
= 3 + (15x4)
= 63 kg per day
Working for 24 hours = approx (60 / 12) x 3 x 24 = 360 kg per 24 hours.
Additional notes to be considered by the business
The semi-continuous dryer requires a higher labour input than the batch dryer due to the
need to remove trays frequently. (See introduction). Additional labour will also be required to
ensure a continuous supply of prepared material for the dryer.
These costs need to be offset against the higher quality product with the semi-continuous
Dryer and greater drying efficiencies.
Packaging
After drying, as described earlier in this manual, the dried material will need to be packaged
in a suitable material, which keeps the product below its critical moisture for a long period of
time. The type of packaging in terms of its ability to protect the product against spoilage will
depend on whether the critical moisture level is high or low and the local climate. For
example it would be possible in a not too humid climate to pack dried dates in paper.
However, this would not be suitable for dried herbs, which would require a plastic packaging
system such as polythene or better still polypropylene.
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