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Agricultural rice dryers employ several drying methods.
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Publication time:
2022-12-07
The operating principle of agricultural dryers is similar; however, the drying process itself may vary, primarily because the moisture content of rice harvested in different regions and at different times can fluctuate. The appropriate drying process should be selected based on the condition of the grain. There are four main drying processes for agricultural dryers, namely:
1. Low-speed drying process
Too rapid drying or too rapid cooling of agricultural products can easily lead to cracking. Compared to high temperatures and low air volume, the increase in cracking rate is less pronounced. However, provided that the increase in the rice cracking rate does not exceed 3%, using low temperatures and high air volumes can boost the drying rate from 1% per hour to 1.8% per hour.
2. Calming baking technique
That is, first the rice is dried, and then it is kept warm for a certain period to allow the internal moisture of the grain to diffuse to the surface, thereby reducing the internal moisture gradient within the grain. After that, a secondary or tertiary drying stage is carried out, which helps to lower the percentage of broken grains. This process requires a judicious selection of the defrosting time.
3. Low-temperature drying technology
The rate of rice cracking during drying depends on the moisture content in the hot air. At the same temperature, if the moisture content in the air is high, the rate of rice cracking decreases. To ensure high-quality rice after drying and reduce the cracking rate, it is necessary to use a lower average temperature—typically below 50°C. Moreover, depending on the type of grain dryer, the temperature of the hot air varies: for example, in counterflow drying, the hot-air temperature can reach over 100°C; in crossflow and mixed-flow drying, it ranges from 45°C to 60°C; and in co-current drying, the temperature should be even lower—around 40°C.
4. High-temperature rapid-drying technology
During the rice harvesting season, when time is relatively limited, it is also worth considering the use of a rapid high-temperature drying process with a rice dryer, employing hot air at a temperature exceeding 100°C to quickly process rice with high moisture content (within 5 minutes). This method allows for a rapid reduction in the rice’s moisture content by 3–5%, after which the heat is maintained to cool the rice. A drawback of this process is that the increased rate of grain breakage may exceed regulatory limits.
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