Background
Organic materials are all subject to microbial attack, but few materials have the sensitivity of seeds. They are mechanically quite sturdy, but when seed moisture content is high, microbes can multiply and destroy the important nutrients they contain. Dehumidifiers allow preservation of rare seeds in scientific applications and they preserve seed value in commercial applications. In developing countries, grain losses in storage can exceed 30% of the crop. By preventing this cause of food shortages, dehumidifiers have the same effect as a 30% increase in crop yield.
Why Moisture Matters?
Moisture content is critical from harvest, through storage, to final sale of cereals and oilseeds. If moisture is too high, there is a risk of quality reduction, or even crop loss in store.
Cereals and oilseeds which are too moist in storage can be subject to:
- Mould growth and mycotoxin production
- Mite infestations, especially in rapeseed
- Heating due to moulds and mites
- Sprouting
Grain which is over-dried before, or during, storage can result in:
- Splitting and cracking
- Impaired quality, particularly in rapeseed
- Wasteful energy use
Grain contracts specify moisture content which, if not met, will result in penalties.
Why Temperature Matters?
Temperatures above 15°C increase the risk of insect and mite populations developing. Grain will be relatively warm post-harvest and is a good insulator, so heat will be lost very slowly. Cooling permits grain to be stored at slightly higher moisture contents and effectively increases the safe storage time. It will also even out or equalize temperature gradients and prevent moisture translocation.
Safety Storage of Grain
Safe storage of grain for longer periods is possible if three conditions are met:
- Grain is maintained at moisture levels of 14% or less;
- Grain is protected from insects, rodents and birds;
- Grain is protected from re-wetting by rain or imbibing moisture from the surrounding air.
The longer the grain needs to be stored, the lower the required moisture content will need to be. Grain stored at moisture contents above 14% may experience the growth of molds, rapid loss of viability and a reduction in eating quality.
Air Conditioning Solutions for Grain Silo
KAWASIMA desiccant dehumidifier is designed to provide dry air continuously and without the high temperatures that could cause damage to the product. Regardless of ambient conditions, the KAWASIMA dehumidifier provides dry air inside the silo that is below the dew point of the air outside the silo, thereby eliminating any condensation and the problems associated with condensation.
Another advantage in using desiccant dehumidification is that the dehumidification can be accomplished with a small, energy efficient dehumidifier. Therefore, there are no problems with bulky equipment and high energy bills.
Depending on the customer’s preference, the KAWASIMA unit can be placed next to the silo or mounted on a catwalk. If desired, multiple silos can be fed from a single dryer in a central drying arrangement or smaller “dedicated” units can be utilized on each individual silo.
General Guidelines
The dehumidifier should be sized to deliver 100% fresh air in an amount equal to at least one air change per hour based on an empty silo.
For low dew point applications, when hygroscopic products could be subject to significant moisture regain, or when interior to exterior temperature differences are more extreme, it is preferable that the fresh air be pre-cooled before dehumidification (chilled water or DX).
If the dehumidification system is designed to re-circulate the silo air, additional filtration may become necessary.