With the improvement of grain planting, the increase of yield per unit area and the increase of national investment in grain drying equipment, the construction of large, medium and small grain drying facilities is more and more. Whether matching high quality, long service life, economic and practical, good reliability and high degree of automation dryer is very important. According to the relative movement direction of grain and airflow, the dryer can be divided into cross flow, mixed flow, smooth flow, and downstream flow, mixed flow, smooth mixed flow and other types.
Cross-flow dryer is the first model introduced in China, mostly cylindrical sieve hole type or square tower sieve type hole structure, there are still a lot of domestic manufacturers production. The advantages of this machine are: simple manufacturing process, easy to install, low cost and high productivity. The disadvantages are: the grain drying uniformity is poor, the unit heat consumption is high, a machine drying a variety of grains is limited, the quality of some grain after drying is difficult to meet the requirements, the internal and external screening holes need to be often cleaned up. But a small circulation dryer can avoid some of the above deficiencies.
Mixed flow dryer is composed of triangle or five corner box staggered (fork) arrangement of the tower structure. The domestic manufacturers of this model are more than cross flow, its advantages are: uniform hot air supply, uniform moisture content of grain after drying; the unit heat consumption is 5% -15% lower; under the same conditions, the drying grain and drying; easy to clean and easy to mix. Disadvantages: complex structure, slightly higher manufacturing cost under the same productivity conditions; a small part of the four corners of the dryer grain precipitation is slow.
Downstream dryer is mostly funnel type inlet and corner box exhaust combined tower structure, it is different from the mixed flow dryer by a main air duct heating air, but by multiple (grade) hot air duct to supply different or part of the same hot air. The number of domestic manufacturers is less than that of mixed current dryer, its advantages are: high temperature can reach 150-250 degrees; low unit heat consumption, can guarantee grain quality after drying; the advantage of reducing large water, and can obtain high productivity; continuous drying, generally up to 10% - 15%; best for drying grain crops and seeds. Disadvantages are: the structure is more complex, the manufacturing cost is close to or slightly higher than the mixed flow dryer; large grain layer thickness, the required high voltage fan power, high price.
Pure upstream dryer production and use is very few, it is mostly used with other air dryer, that is, for downstream or mixed flow dryer cooling section, the formation of downstream and mixed flow dryer. The advantages of countercurrent cooling are that the natural cold air can fully contact with the grain, which can increase the cooling speed and appropriately reduce the height of the cooling section. Subcurrent, mixed current and mixed current dryer are respectively the use of their own advantages, in order to achieve high temperature fast drying, improve drying ability, do not increase the unit heat consumption, ensure the quality of grain and moisture content uniform.