Methods for reducing consumption of grain drying equipment
In most parts of China, the post harvest moisture content of grain is generally higher than the safe moisture content (14%), which is not conducive to storage and preservation. Using natural precipitation not only takes up time, effort, and space, but also makes it difficult to achieve the desired effect. Therefore, many grain depots use artificial precipitation.
According to the method of grain drying, dryers can be divided into:; Convection heat dryer, conduction dryer, radiation dryer, and high-frequency electric field dryer, etc. Among them, the conduction drying dryer was widely adopted by grain enterprises in the 1980s and early 1990s. This type of dryer is also known as a steam boiler, grain storage bin, preheating tower, drying tower, cooling tower, and various conveying equipment. Its advantages are: high precipitation, which can reduce water content by 10% -15% in one go, large production capacity, and high degree of automation. Its disadvantages are high cost, high fuel consumption, and inconvenient maintenance.
The working principle of this dryer is:
This drying method does not directly contact the steam with the grain, but only passes through a metal pipeline. The grain flows outside the pipeline and absorbs heat. After being heated, the temperature of the grain increases, causing the internal moisture to transfer. The surface vaporizes and the vaporized moisture is carried away by the drying medium, thereby reducing the moisture content of the grain.
According to its working principle, the methods for reducing consumption are as follows:
1. Improve the drying medium. The substance that can be mixed with water vapor and carried away during grain drying is called the drying medium. According to the definition of drying medium, if the drying medium can heat the grains during the drying process to a large extent; And take away the constantly vaporized water vapor, so that the grain can be dried. And this depends on the capacity of the drying medium for water vapor, that is, the humidity of the air. The humidity of air at different temperatures varies. At a certain temperature, humid air has a certain limit to the amount of water vapor it can hold. When the amount of water vapor held in the atmosphere reaches dynamic equilibrium with the amount of water vapor condensed into water in the air, the amount of water vapor it can hold reaches its upper limit. At this point, the air is called saturated air, and its humidity is called saturated humidity. The same type of air has different saturation humidity values at different humidity levels. For example, the saturation humidity value at 20 ℃ is 17.2 g/m3, while at 34 ℃ it is 37.3 g/m3. It can be seen that the higher the saturation humidity value, the stronger the drying ability.
Traditional steam dryers release flue gas into the steam after passing through a preheating tower, which not only pollutes the environment but also wastes heat energy. To improve the efficiency of thermal energy utilization, flue gas can be directly used as the drying medium. The specific renovation method is to preheat the flue gas and directly introduce it into the heating tower from the flue box. This can effectively increase the temperature of the drying medium 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, it will affect the quality of the grain. Generally, the temperature of the drying medium should be controlled between 80 ℃ and 130 ℃.
2. Adopting the drying ventilation drying method. In traditional drying methods, grains are usually dried to a moisture content of 14% -15% and then cooled for storage. The drying ventilation drying method first applies high-temperature drying to the grains. Reduce the moisture content to 18%, and then send the grain with this moisture content into the warehouse for 5-7 hours to allow the temperature and moisture between the interior and surface of the grain to reach equilibrium. Then, slowly ventilate it with an air volume of 25m3 to 50 m3/h for about 8 hours to make the temperature of the grain the same as the atmospheric temperature. Generally, the higher the temperature of the grain entering the warehouse, the more moisture is removed (about 4%).
The advantages of this method are:
(1) Increase the drying capacity. Due to the decrease in moisture content to 18% instead of 14%;
(2) Reduce energy consumption. Because the precipitation rate of grain inside the equipment is low; During the slow ventilation process, the accumulated heat energy of the grain itself is utilized to further reduce precipitation.
(3) Ensure the quality of food. Because direct cooling of dried grains often causes grain breakage, using this method can reduce the breakage rate and breakage rate;
(4) Using this method can reduce drying costs by about 13%.
