2. Mechanical drying (or) artificial drying

2. Mechanical drying (or) artificial drying

    • Forced air is used for seed drying by the following three means.
    a. Natural air drying
    • Natural air is blown upon the seeds using suitable air blower for drying.
    • Continuous drying is possible in this method.
    • In modern seed godowns provisions are made to forcible circulation of air with the help of electric blower or fan.
    • If the outer air is comparatively dry, this method is followed.
    • So it is possible only during dry months.
    b. Drying with supplemental heat
    • Small quantity of heat is applied to raise the air temp to 10-20° F for reducing the relative humidity of air used for drying.
    • In this, drying is performed quickly due to use of dry air, but continuous drying for long period affects seed quality.
    c. Heated air Drying
    • The air is heated considerably as much as by 100° F (40° C) and used for drying the seeds.
    • Very quickly the seeds get dried.
    • The seeds should not be continuously dried as it causes damage to seed.
    • High moisture seeds should be dried by this method.
    Advantages
    • Quick method
    • Perfect drying is possible even under unfavourable weather condition.
    • Seed loss is minimized.
    Disadvantages
    • Requires specialized equipment and machine, which is costly.
    • Care should be taken while drying the seed using hot air, as it causes damage to the seed.
    • Tempering is to be followed while drying the seed in this method.
    Types of drier
    1. Metal bin drier
    2. Vegetable seed drier
    3. Batch drier
    • Here the seeds are placed in a metal bin and the heated air is blown in to the bin through the perforations made at the bottom of the bin. In this uniform drying of all layer is not possible for which decide the thickness of the seed layer to be taken to the bin and also have to stir the seed manually or mechanically at regular intervals.
    Vegetable seed drier
    • In this drier, the seeds are separated over the bottom screen seed trays which are kept inside chamber or cabin. The heated air is passed to dry the seed. The heat is generated by electrical source and the air is passed through trays. Here uniform drying is possible.
    Batch-Drier
    • In bin batch dryers, the seed is placed in a (usually round) bin, and ambient or slightly heated air is blown through it by a fan. The maximum thickness of the seed layer in the bin depends on the initial moisture content, the type of seed, the air temperature and RH and fan horse power. To obtain a uniform airflow through the seeds, a full perforated floor is required.
    • A layer of seed 0.8 to1.0 m at 20% moisture can be dried to 14% within 24 hrs without affecting germination at 30-35°C and 50-60%RH air at a rate of 5-8m3 per minute per m3 of seed.
    • After the seed in a bin has reached the acceptable average moisture content, a moisture gradient will remain from the top to the bottom of the seed. The surface layer will have a moisture content above the average and the bottom layer of the bin will be lower than average. Thus, proper mixing of the seeds is essential before further storage or packaging. This can be addressed by installing one or more grain stirrers to mix the entire content of a bin for 3-12 hours.
    Wagon Batch- Dryer
    • A seed transport wagon can be transformed into a wagon batch-dryer by equipping it with a plenum, a perforated floor, and a fan/heater unit coupled with a canvas transition to the wagon.
    • The drying principles of a wagon batch dryer and a bin batch dryer are similar.
    • Wagon batch dryers are most frequently used for drying fragile seeds such as large-seeded legumes (eg. field or garden beans and peanuts).
    • The recommended air flow rate for the ambient –air wagon drying of a 1.5m layer of peanut seeds is 0.25m3 of air per m2 of floor area.

Last modified: Wednesday, 20 June 2012, 6:49 AM