How to use the DRYIT semi-continuous tray dryer
Practical Action
The Dryit range of dryers
Batch dryer
The batch dryer is shown in the diagram above. The drying chamber is divided into two
compartments each holding 48 trays 4' x 3' .The trays are arranged so as to force the air to
follow a zigzag path. This double chamber is recommended as it allows greater flexibility. If
only a small amount is to be dried only one chamber can be used and obviously two different
products can be dried at the same time. Air supplied from the heater-blower can be diverted
to one or both chambers by means of a simple flap. Most users construct a frame in 3” x 2"
timber, which is clad in plywood. The chamber should be supported off the floor to reduce
heat losses and preferably insulated.
Cost constructed in the UK approximately £1700 including heater and thermostat
Capacity for herbs: approximately 250kg/day
Heat source: 60kW, 2800 m3/hr (200,000 BTU, 1650 cfm) heater blower. Such heaters
cost approximately £1100. If kerosene fired the heater must be indirect -that is have a heat
exchanger so that the gases of combustion are removed by a chimney.
Semi-continuous Tray Dryer
The drying chamber holds up to 16 trays approx 3ft x 4ft. Constructed from angle iron and
steel bar and clad with plywood. When used for herbs a typical tray change time is 15 to 20
minutes.
• Cost (UK constructed): £3000
• Capacity: approximately 350 kg/day with herbs
• Heat source as for batch dryer
• Medium semi-continuous tray dryer
This is a recent development and is essentially a half-sized version of the SC above. The
main structure is of wood with the minimum of metal parts. The chamber holds up to 12
trays each 90cm x 70cm
• Cost: in UK £1000
• Capacity: approximately 70 kg/day
• Heat source 14-41 kW, 680m3/hr (48,000 to 140,000 BTU, 400cfm) gas fired
blower. Heaters of this size cost approximately £300.
Some economic considerations
It is clearly of crucial importance for any small business to understand how to calculate and
analyse its costs in order to:
• Be sure that the business is profitable
• To analyse where cost savings and investment are
• Best introduced
• To carry out rough preliminary costings for a new product line.
This section does not attempt to follow, or replace, the traditional cash flow, internal rate of
return types of calculations typically prepared by banks etc. Its aim is to concentrate on
some practical aspects that will allow the business to gather raw data for the preparation of a
conventional business plan.
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