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The problem of drying and storing onions in the tropics is solved, in an energy efficient way. Thanks to condense drying using VaccTek. Everything is explained here!
As an example, let's take a look at Indore in India.
In Indore, onions are harvested between the end of the dry season and the beginning of the monsoon season. Onions are sold at very low prices during the harvest, not only because there is such a high supply of onions in the area, but also because farmers lack adequate storage facilities and are forced to sell their produce quickly before the monsoons start and cause it to rot.
On average, as much as 50% of the onion harvest in Indore is lost, and sometimes this percentage is even higher. For further information, see: Financial losses incurred by inadequate storage. Have a look: Financial losses incurred by inadequate storage..
Whilst many cold stores for potatoes can be found in the area, none can be found for onions.
This comes as no surprise to us.
Potatoes have to be kept cold at all times. To find out why, visit: Potato Storage. How to store potatoes long term?.
Onions do not always have to be stored at low temperatures; they can be stored at 2° Celsius as they are in the north of Europe, but they can also be stored at 25 to 30° Celsius..
Winters are very cold in the north of Europe, with temperatures generally ranging from -5° to 5° Celsius. Hence, storing onions at 2° Celsius in these conditions is very energy efficient.
However, even in northern Europe, onions have to be heated to just above the local dewpoint temperature before they are sold so as to avoid condensation and them becoming too wet during transit.
However, in the tropics, it would be madness to store produce at 2° Celsius, when it can be stored at between 25° and 30° Celsius.
Consider the following table:
|Storing onions at 2° Celsius||Storing onions at 30° Celsius|
|Energy wasted cooling down||Specific heat contents of onion per tonne X Delta T X number of tonnes (kWh)||Almost 0 kWh, we hardly change the temperature.|
|Energy needed to dry onions||XX kWh needed to evaporate a certain amount of water.||XX kWh needed to evaporate a certain amount of water.|
|Energy wasted to offset heat energy lost through the walls of the storage facility||Here we offset the heat lost with a Delta T of about 30° Celsius||Here we offset the heat lost with a Delta T of about 0 ° Celsius|
|Energy wasted to warm up the onions||Specific heat contents of onion per tonne X Delta T X number of tonnes (kWh)||Close to 0 kWh, we hardly change the temperature.|
Why a constant temperature?
An onion, even in storage, is a living thing. Every time the temperature changes it will start sprouting.
Why total darkness?
An onion, even in storage, is a living thing. Every time it is exposed to light it will start sprouting.
Why as little ventilation as possible?
Only the CO2 between the onions should be removed, otherwise they continue to breathe and will sprout again. And every time we ventilate using air with a humidity of 65% they will lose some water, even though they are sealed.
Why a relative humidity of 65%?
This dryness is to keep bacteria and fungi at bay. Bacteria and fungi are not killed by dryness, but they remain more or less dormant.
For more details see:
Drying onions: common truths and misconceptions: and the sub-sections within this section
To successfully store freshly harvested, humid onions for a long period of time at around 30° Celsius in an environment where the temperature is also 30° Celsius and the relative humidity is around 80%, the onions have to be dried very quickly at a constant temperature, and then kept at 30° Celsius with an ambient relative humidity of 65% and an outside relative humidity of at least 95%.
VaccTek. is the answer. For more information see the full section and sub-sections here: Drying onions: common truths and misconceptions
Instead of using warm or cold air (heating or cooling the onions) we create an environment with a temperature of 30°C, and a relative humidity which is about 55% during the drying period, and rises to 65% during storage.
This way, no energy is wasted on heating or cooling the onions.
VaccTek sucks in the very humid, warm air from outside and cools it down to far below the local dewpoint. As a result, the water is extracted from this air via condensation.
Next, 80 to 95% of the heat generated by the cooling equipment is transferred back into the cooled, dried air. As a result, the air entering the facility from the VaccTek unit has a temperature of 30°C and a relative humidity of 55 to 66%.
Consequently, we only use energy to evaporate the moisture from the onions, but never change their temperature. This is ideal for onions.
If you remember your thermodynamics, you will understand that we reuse 80 to 95% of the energy that is enclosed in the cooling system's enthalpy diagram. And if you really remember your thermodynamics, you will realise that we hardly raise the entropy of the universe with this system.
VaccTek dries by regulating the relative humidity of the air, while keeping the air temperature constant.
To mechanise your post harvest processes:
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