How to use the DRYIT semi-continuous tray dryer
Practical Action
Figure 3: Graph to show fuel use with drying temperature
ID 200 kerosene fired burner. Fuel pump rate 1.6 gall/hr as used in the batch dryer and SC.
Max temp lift above ambient 70 °C.
Thus if the ambient temperature is 25ºC the air temperature from the burner will be 95ºC
with the heater running full heat (all the time). The consumption will thus be 1.6 gall/hr. If
the thermostat is set at 25ºC the burner will not provide any heat, so fuel use will be zero.
This can be plotted on a graph and fuel use at any temperature read off with ease.
In the case of propane gas fired burners the simplest way is to weigh the cylinder to measure
gas usage. Again a simple graph of fuel use against temperature can be prepared by
experimentation.
Labour costs
These are fairly straightforward to calculate. Is worth stressing however that semi-continuous
drying does involve 24 hr working. The following points need to be thought about:
Is shift working socially acceptable? What level of shift pay is involved?
The labour cost per kg of final product should be worked out for both batch and semi-
continuous bearing in mind that semi-continuous has a greater throughput and uses less fuel
Is a night watchman employed in the plant? Could he work the dryer?
Is the quality better in semi-continuous? Does this actually matter?
Packaging
Packaging can represent a major cost: often due to having to buy it in large amounts, which
ties up a considerable amount of capital. Good packaging and presentation however a vital
matter for producers. In many cases the pack is the first point of contact with the buyer and
the message it gives can lead to a sale.
It is strongly recommended that expert advice is obtained initially on the best technical
package to protect the dry food through its shelf life. The design etc should then follow.
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