1. Cross flow dryer
The cross-flow dryer is the first model introduced in our country, mostly cylindrical or square-tower sieve structure, and there are still many domestic manufacturers producing it.
The advantages of this machine are: simple manufacturing process, convenient installation, low cost and high productivity. The disadvantages are: poor uniformity of grain drying, high unit heat consumption, limited drying of a variety of grains in one machine, difficult to meet the quality requirements of some grains after drying, and frequent cleaning of the inner and outer sieve holes. However, a small circulating dryer can avoid some of the above-mentioned shortcomings.
2. Mixed flow dryer
Mixed-flow dryers are mostly tower structures composed of triangular or pentagonal boxes staggered (forked). There are more domestic manufacturers of this model than cross-flow. Compared with cross-flow, its advantages are: (1) The supply of hot air is even, and the moisture content of the grain after drying is more uniform; (2) The unit heat consumption is lower by 5% to 15%; 3) The fan power required under the same conditions is small, and the unit consumption of drying medium is also small; (4) There are wide varieties of dried grains, which can dry grains and seeds; (5) It is easy to clean and not easy to mix.
The disadvantages are: (1) The structure is complex, and the manufacturing cost is slightly higher under the same productivity; (2) The precipitation of a small part of the grains at the four corners of the dryer is slow.
3. Downstream dryer
Downstream dryers are mostly tower structures that combine funnel-type air inlets and angular box exhaust ducts. It is different from mixed-flow dryers that use one main air duct to supply hot air, but instead consists of multiple (stages). The hot air pipe supplies different or partly the same hot air.
The number of domestic manufacturers is less than that of mixed-flow dryer manufacturers. Its advantages are: (1) The hot air temperature is high, and the temperature in the first-level high temperature section can reach 150～250℃; (2) The unit heat consumption is low, which can guarantee the dried grain Quality; (3) Dryers with three-level downstream and above have the advantage of reducing large water content and can obtain higher productivity; (4) A large precipitation range during continuous drying, generally up to 10% to 15% ; (5) Most suitable for drying food crops and seeds with high moisture content.
The disadvantages are: (1) The structure is relatively complicated, and the manufacturing cost is close to or slightly higher than that of the mixed flow dryer; (2) The thickness of the grain layer is large, the required high-pressure fan power is large, and the price is high.
4. Drying machines for forward and countercurrent, mixed countercurrent and forward mixed flow
Pure countercurrent dryers are rarely produced and used. Most of them are used in conjunction with dryers with other airflows, that is, used in the cooling section of co-current or mixed-flow dryers to form co-current and mixed counter-current dryers. The advantage of countercurrent cooling is that the natural cold wind can fully contact the grain, which can increase the cooling speed and appropriately reduce the height of the cooling section. The forward and countercurrent, mixed countercurrent and forward mixed flow dryers use their respective advantages to achieve high-temperature and rapid drying, improve drying capacity, without increasing unit heat consumption, and ensuring uniform grain quality and moisture content.