Human settlements

Renewable energy

Solar thermal 07: Solar energy can be harnessed to cool grains

Renewable energy commercialisation in Australia

A new type of grain-cooling device that harnesses the sun's energy is being developed. The system is simple to operate, will help to store grains in excellent condition and will control insect pests.

Cooling stored grain helps to preserve desirable qualities such as seed viability, and keeps insect populations under control. Aeration has proved to be a useful tool for cooling grains. However, the warm night temperatures that occur in many important grain-growing regions of Australia compromise its effectiveness.

The need to cool grains to lower temperatures is motivating the development of a system that is almost as simple as conventional aeration, but which is more effective. With the support of a $370,000 grant under the Renewable Energy Commercialisation Program, A.F. Gason Pty Ltd of Ararat, Nelson Silos of Rochester and the Victorian University of Technology have collaborated to develop the new unit.

During conventional aeration the water in the air condenses and gives out heat, with the result that the grains cannot cool to the same temperature as the air entering the grain store. An answer to this problem is to remove the humidity in the air before it enters the grains. This is precisely what the new grain cooling device does. The moisture is removed from the aeration air in the same way that moisture is often removed from binoculars and cameras to prevent them from being ruined by condensation. In the grain cooling system, silica gel is placed in channels through which cool but humid air flows at night, as shown in Figure 1a. Because the silica gel is dry it absorbs moisture and gives out heat (the opposite to evaporation). This heat is removed from the silica gel by means of a second air stream that flows on the outside of the channels that contain the silica gel. This is the same heat that is normally liberated inside the silo when grains are aerated with moist air.

After the nightly cooling cycle the silica gel is wet, and this is where solar energy comes into the picture. The silica gel is dried out during the day by forcing heated air through it, and after this air has picked up moisture it is expelled to the atmosphere as shown in Figure 1b. The silica gel is said to have been regenerated. During the regeneration process the air needs to be heated to about 55C, and this is conveniently achieved using a solar collector.

Figure 1a: The operation of the new grain cooling system during the night, and Figure 1b: The operation of the new grain cooling system during the day cycle are available in the attached PDF file.



For more information please contact

David Whitehead
Nelson Silos
Kyabram Rd
Rochester VIC 3561
Tel (03) 9842 2066
Fax (03) 9846 5377

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