In the case of stationary type drying in rack drying systems, as the depth of paddy is relatively wide and ranges from 400 to 800 mm, drying speed is limited to prevent over-drying in the lower grain portion which is located on the air blowing side. In order to increase the drying speed while maintaining the quality of grains, the grain heating/drying system which raises the temperature of grains prior to ventilation was developed and evaluated. The results of evaluation tests are as follows: 1. The grains of entire depth were dried for one hour from the beginning of drying. The drying speed has increased 15% as compared with the conventional drying without heating. 2. The effect of heating becomes smaller as the moisture content of paddy is lower. Therefore, the energy efficiency of the system is higher when more heating processes in number with less ventilation period are applied at a higher moisture content, and no heating is applied at a lower moisture content. 3. When the grains are heated after mixing and then tempered, the moisture migration in a grain is expedited and the variation of moisture contents on dried grains becomes smaller. This effect is larger when the initial moisture content of paddy is higher. 4. The difference of moisture contents between the simulation of grain heating/drying, and the experiments was 0.22-0.53% on wet basis. Therefore, it has been confirmed that this simulation is useful to estimate the drying speed on the grain heating/drying system.
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