Drying principle of dryer and precautions for purchase and use
The use of mechanical drying of agricultural products has many advantages, such as short drying time, strong drying ability, low drying cost, and resistance to natural disasters. In particular, in recent years, the electrical control of the drying equipment has been realized, and the operation and use are simple, and the quality of the agricultural product after drying is ensured. Therefore, the drying trend of China's agricultural products is gradually replacing traditional natural methods by mechanical drying. Now we have a number of large-scale production enterprises, such as China Agricultural Mechanization Research Institute, Fuzhou Sanfa Drying Equipment Co., Ltd., Shanghai Sanjiu Machinery Co., Ltd. Ltd., Gold Agricultural Machinery (Wuxi) Co., Ltd. and other enterprises.
1. Drying principle and classification
(1) Drying principle Drying refers to reducing the moisture contained in agricultural products to a certain extent by physical means, which is beneficial to storage and quality. At present, the commonly used drying technologies mainly include thermal convection drying, far infrared radiation drying, high frequency drying, microwave drying, and solar drying.
Thermal convection drying is to heat and dehumidify agricultural products by using hot air or hot flue gas as a medium for drying;
Thermal conduction drying is the exchange of heat by heat exchange to dry agricultural products;
Far-infrared radiation drying is the far-infrared invisible light wave emitted by the infrared emitter to irradiate the agricultural product, so that the water molecules of the agricultural product generate intense vibration and heat up, thereby achieving the purpose of drying;
The principle of high-frequency drying and microwave drying is the same. Electromagnetic waves generated by high-frequency electric fields or microwave electric fields are used to irradiate agricultural products. High-frequency electromagnetic waves or microwave electromagnetic waves cause rapid polarity transformation of water molecules in materials, thereby generating thermal effects. Distribute the water to achieve the purpose of drying.
(2) Classification of dryers According to different drying principles, commonly used drying machinery and equipment include room temperature ventilation drying chamber, thermal convection dryer, far infrared radiation dryer and solar collector drying chamber, among which the most used thermal convection dryer widely.
The thermal convection dryer can be classified as follows: 1 According to the temperature of the airflow, it can be divided into a low temperature slow dryer and a high temperature fast dryer; 2 according to the state of the agricultural products in the drying room can be divided into fixed bed, moving bed, fluidized bed , spouted bed and other types; 3 according to the structure of the drying chamber can be divided into flat bed, cylinder, column, tower, drum type, etc.; 4 according to the operation can be divided into continuous, intermittent and cyclic ; 5 according to the direction of grain movement, cross-flow dryer, downstream dryer, counter-flow dryer, mixed flow dryer.
(3) Hot air stove
The thermal convection dryer uses air as the medium, that is, the heated air is transferred to the material, the material is evaporated by the heat, and then taken away by the air to achieve the purpose of drying. Therefore, the heat supply device of the heat convection dryer is called hot air. furnace. According to the heating mode, the hot blast stove is divided into a hot blast stove directly supplying furnace gas and a hot blast stove indirectly supplying hot air. According to the fuel, there are mainly hand furnaces, gas furnaces, straw gasification furnaces, and fuel heat exchange furnaces. The hand-burning furnace uses anthracite, firewood, etc. as fuel, and adopts direct heating method; the gas furnace uses coal as fuel to generate gas for combustion, and the flue gas is mixed with cold air to enter the dryer, and the material is basically not polluted; The chemical furnace is made of straw as raw material, and the hot air generated by the combustion after gasification enters the dryer. The material is basically not polluted. The fuel heat exchange furnace is burned with diesel or kerosene as fuel, and the generated hot air is directly or through exchange. The hot air generated by the heat device enters the dryer, and there are two types, direct and indirect. Due to the use of diesel or kerosene, the running cost is high.
2. Purchase principle
The type of dryer and the drying method are various, and the materials to be dried are also very different. Therefore, it is very important to select a drying machine suitable for drying materials and drying purposes.
(1) Drying object
The choice of dryer should be based on the physical properties, thermal sensitivity, fluidity, and ease of destruction of the material in the wet state. The form of agricultural products in wet state can be divided into liquid, such as milk, spray dryer can be used; granular form, such as grain, its fluidity is good and resistant to sputum, tower high temperature dryer can be used, low temperature can also be used Dryer to obtain better quality; there are certain size, such as mushrooms, fungus, chrysanthemum, etc., its shape is easy to be destroyed, it is better to use drying equipment in static state, such as cabinet dryer, flat bed dryer, far Infrared dryer, etc.
(2) Economic conditions
Good economic conditions, you can use a dryer with automatic control of the microcomputer. This type of machine can be automatically dried as long as the drying program is set, which reduces the labor intensity of the operator and ensures the dry quality of the agricultural products. Some simple dryers are chosen for poor economic conditions.
(3) Energy conditions
When choosing a dryer, consider the local energy situation and make the most of local resources. For local coal, there are many dryers that can use coal as fuel; in plain areas, orange-rod gasification dryers can be considered; in mountainous areas, wood-fired dryers can be considered.
(4) Other conditions
If there are available warehouses, the initial investment can be reduced. Purchase brand-name products with professional factory production, good after-sales service and complete certificates.
3. Precautions for use
(1) After purchasing the equipment, the user should check all the parts, accessories and accompanying vulnerable parts, special tools and product instruction manual, quality inspection certificate, warranty and so on.
(2) When installing the equipment, the hot blast stove, fan, drying body, conveying pipeline, etc. should be aligned, and the connection is tight and seamless, so as to avoid entering too much cold air and causing air leakage.
(3) Installation is completed. Close the power switch and run the rotating parts such as hot air blower and air cooler. Observe the direction of rotation. If there is a reversal, correct it immediately.
(4) It should be noted during use: 1 The agricultural products entering the drying equipment must be removed from weeds with a length of 5 cm or more, and the cleanliness of the materials is above 90%, otherwise it will cause blockage. 2 During the drying process, the hot air temperature must be within the range required by the process. If the temperature is lower than the specified range, the drying effect of the material is poor and the productivity is low. If the temperature is higher than the specified temperature, the quality of the product may be seriously affected, and even the burnt gas may be generated. The phenomenon. The heating temperature of various agricultural products in the dryer is different, the rice and corn are below 50 °C, the wheat is below 60 °C, and the rapeseed is below 60 °C ~ 70 °C. 3Measure the initial moisture of the agricultural products before drying, and send the agricultural products with different moisture to the equipment and dry them separately to avoid the uneven moisture of the dried products and affect the product quality.
(5) The new technical equipment should be trained immediately after the purchase of new equipment, and special personnel should be repaired and maintained.