FARMER'S NOTEBOOK
Multi-source dryer for copra
AGRICULTURE CORRESPONDENT
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The solar dryer can also be run on electricity and a host of biofuels such as coconut husk and shell.
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SCIENTISTS AT the Central Plantation Crops Research Institute (CPCRI), Kasaragod, Kerala, have developed a simple multi-source dryer for copra.
It is essentially a solar dryer, which can also be run on electricity and a host of biofuels such as coconut husk and shell as sources of energy, according to Mr. K. Madhavan, Mr. S.J.D. Bosco and G. S. Hareesh, who designed this copra dryer.
Infection prone
Coconut endosperm is exposed while drying and is prone to fungal and bacterial infections if the drying air temperature falls below 38 degrees Celsius.
Moreover, fresh coconut will have moisture content ranging from 45 to 50 per cent, and once the endosperm is open drying should start within four hours to prevent bacterial attack.
The moisture level should be brought down to 20-25 per cent within the short time.
The new dryer is designed to meet the specific needs of copra drying. It is primarily a solar dryer with electrical energy as a back up. A separate heating chamber using biofuels is provided to substitute electric heaters.
Dryer parts
The dryer consists of a semi-circular double pass flat plate solar collector having a transparent cover made of 200-micron UV film; an absorber plate made of 250-micron agrifilm; and a bottom casing made of 26 gauge galvanised iron sheet.
The drying chamberhas a radius of 1.5 metres. In order to have maximum solar incidence, the solar dryer is fixed in such a way that its curved surface is oriented towards north/south.
Two trolleys are provided to hold the trays to keep the coconut for drying. The heater assembly has six 1000 watts heaters, a blower to draw hot air from solar collector and heaters to the drying chamber, and an electronic control system.
The blower motor is fixed outside the dryer, but the heater assembly is kept inside the drying chamber thereby avoiding extra insulation.
The heating chamber consists of mainly three compartments — the fuel chamber, air-preheating chamber and air-heating chamber. The pre-heated air will enter the middle compartment where it is heated up to the maximum. A chute with butterfly valve for entry of fresh air is provided in the conical section of the heating unit to control the temperature at the outlet manually.
The fuel capacity was 4 kg husk or 8 kg shell. An electronic temperature control system is also designed to retain the temperature in the drying chamber within the set limits, according to the scientists.
Drying trials were conducted with 2000 coconuts per batch and the drying time taken was 22 t0 24 hours in both cases.
The electrical energy consumption depends on the number of sunshine hours on a particular day.
Whenever the temperature inside the drying chamber falls below 40 degrees Celsius or any other set limit, the heaters are switched on by the electronic switching circuit.
The temperature raised up to 53 degrees Celsius when the electronic switching circuit cuts electric supply to the heaters.
The cost of the dryer was estimated to be Rs 40,000, and with the fuel attachment it is likely to cost Rs. 47,500.
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