In most parts of China, post-harvest food moisture is generally higher than safe moisture (14%), which is not conducive to safekeeping and storage. The use of natural precipitation not only takes time, effort, and space, but it is also difficult to achieve the desired effect. As a result, many food banks use artificial precipitation.
According to the method of grain drying, the dryer can be divided into convection heat dryer, conductive drying dryer, radiation dryer and high frequency electric field dryer. Among them, the conductive drying dryer was commonly used by grain companies in the 1980s and early 1990s. This type of dryer consists of steam boilers, storage silos, preheating towers, drying towers, cooling towers, and various transportation equipment. Its advantages are: large amount of precipitation, which can reduce moisture by 10%-15% at a time, and has a large production volume and a high degree of automation. The disadvantages are high cost, large fuel consumption, and inconvenient maintenance.
From the grain drying process chart, we can see that this kind of drying method does not directly contact the grain with steam. It is only through the metal pipe. The grain flows outside the pipe and absorbs heat. After the grain is heated, the temperature of the grain rises, causing the internal water to transfer, and the surface is vaporized and vaporized. The water is taken away by the drying medium, thereby reducing the moisture content of the grain.
According to its working principle, the consumption reduction methods are as follows:
1, improve the drying medium. When grain is dry, substances that can mix with water vapor and carry it away are called drying media. According to the definition of the drying medium, if the drying medium can maximize the heating of the food in the drying process and take away the continuously vaporized water vapor, the grain can be dried. This depends on the package capacity of the drying medium on the water vapor, ie the absolute humidity of the air. The absolute humidity of air at different temperatures is different. At a certain temperature, the amount of water vapor contained in the humid air has a certain limit. When the amount of water vapor contained in the atmosphere and the amount of water vapor in the air condense into water, the water accommodates the water. The maximum amount of steam is reached. At this time, the air is called saturated air, and its absolute humidity is called absolute saturation humidity. The same kind of air has different saturation humidity values ​​at different humidity, such as a saturated humidity of 17.2 g/m3 at 20°C and 37.3 g/m3 at 34°C. It can be seen that the greater the saturated humidity value, the stronger the drying ability.
In a conventional steam dryer, the flue gas enters the large steam after passing through the preheating tower, which not only pollutes the environment but also wastes heat energy. In order to improve the use of heat energy, flue gas can be directly used as a drying medium. The specific transformation method is to directly introduce the flue gas from the smoke box into the heating tower after being warmed up. In this way, the temperature of the drying medium can be most effectively increased without increasing the heat source. It should be noted that the temperature of the furnace gas should be taken into account during production. If the temperature is too high, the quality of the grain will be affected. Under normal circumstances, the temperature of the drying medium should be controlled between 80°C and 130°C.
2, using drying - ventilation drying method. In the traditional drying method, the grain is usually dried to a moisture content of 14%-15%, and then stored under cooling. The drying-ventilating drying method firstly heats the grain at a high temperature to reduce the moisture to 18%, and then the water is dried. Grain is fed into the warehouse for 5-7 hours to slow the temperature, so that the temperature and moisture in the grain and the surface of the grain tend to balance. Then it is slowly ventilated, the air volume is 25m3 to 50m3/h, and the ventilation time is about 8 hours. The temperature of the grain is the same as the temperature of the atmosphere. The higher the temperature of the grain that normally enters the tank, the more water is removed (about 4%).
The advantages of this method are: (1) Increase the amount of drying. Decrease water consumption to 18% instead of 14%; (2) Reduce energy consumption. Because of the low precipitation rate of grain in the equipment, in the process of slowing the Soviet Union, during the slow ventilation, the heat energy accumulated by the grain itself will be used to further precipitation; (3) Guarantee the quality of grain. Because the direct cooling of grain after baking often results in the explosion of grains, the use of this method can reduce the bursting rate and crushing rate. (4) This method can reduce the drying cost by 13%.
According to the method of grain drying, the dryer can be divided into convection heat dryer, conductive drying dryer, radiation dryer and high frequency electric field dryer. Among them, the conductive drying dryer was commonly used by grain companies in the 1980s and early 1990s. This type of dryer consists of steam boilers, storage silos, preheating towers, drying towers, cooling towers, and various transportation equipment. Its advantages are: large amount of precipitation, which can reduce moisture by 10%-15% at a time, and has a large production volume and a high degree of automation. The disadvantages are high cost, large fuel consumption, and inconvenient maintenance.
From the grain drying process chart, we can see that this kind of drying method does not directly contact the grain with steam. It is only through the metal pipe. The grain flows outside the pipe and absorbs heat. After the grain is heated, the temperature of the grain rises, causing the internal water to transfer, and the surface is vaporized and vaporized. The water is taken away by the drying medium, thereby reducing the moisture content of the grain.
According to its working principle, the consumption reduction methods are as follows:
1, improve the drying medium. When grain is dry, substances that can mix with water vapor and carry it away are called drying media. According to the definition of the drying medium, if the drying medium can maximize the heating of the food in the drying process and take away the continuously vaporized water vapor, the grain can be dried. This depends on the package capacity of the drying medium on the water vapor, ie the absolute humidity of the air. The absolute humidity of air at different temperatures is different. At a certain temperature, the amount of water vapor contained in the humid air has a certain limit. When the amount of water vapor contained in the atmosphere and the amount of water vapor in the air condense into water, the water accommodates the water. The maximum amount of steam is reached. At this time, the air is called saturated air, and its absolute humidity is called absolute saturation humidity. The same kind of air has different saturation humidity values ​​at different humidity, such as a saturated humidity of 17.2 g/m3 at 20°C and 37.3 g/m3 at 34°C. It can be seen that the greater the saturated humidity value, the stronger the drying ability.
In a conventional steam dryer, the flue gas enters the large steam after passing through the preheating tower, which not only pollutes the environment but also wastes heat energy. In order to improve the use of heat energy, flue gas can be directly used as a drying medium. The specific transformation method is to directly introduce the flue gas from the smoke box into the heating tower after being warmed up. In this way, the temperature of the drying medium can be most effectively increased without increasing the heat source. It should be noted that the temperature of the furnace gas should be taken into account during production. If the temperature is too high, the quality of the grain will be affected. Under normal circumstances, the temperature of the drying medium should be controlled between 80°C and 130°C.
2, using drying - ventilation drying method. In the traditional drying method, the grain is usually dried to a moisture content of 14%-15%, and then stored under cooling. The drying-ventilating drying method firstly heats the grain at a high temperature to reduce the moisture to 18%, and then the water is dried. Grain is fed into the warehouse for 5-7 hours to slow the temperature, so that the temperature and moisture in the grain and the surface of the grain tend to balance. Then it is slowly ventilated, the air volume is 25m3 to 50m3/h, and the ventilation time is about 8 hours. The temperature of the grain is the same as the temperature of the atmosphere. The higher the temperature of the grain that normally enters the tank, the more water is removed (about 4%).
The advantages of this method are: (1) Increase the amount of drying. Decrease water consumption to 18% instead of 14%; (2) Reduce energy consumption. Because of the low precipitation rate of grain in the equipment, in the process of slowing the Soviet Union, during the slow ventilation, the heat energy accumulated by the grain itself will be used to further precipitation; (3) Guarantee the quality of grain. Because the direct cooling of grain after baking often results in the explosion of grains, the use of this method can reduce the bursting rate and crushing rate. (4) This method can reduce the drying cost by 13%.