Methods of reducing consumption of grain drying equipment

In most areas of China, the post harvest moisture of grain is generally higher than the safe moisture (14%), which is not conducive to storage and storage. Therefore, many grain depots use artificial precipitation.

According to the method of grain drying, the dryer can be divided into convection heat dryer, conduction dryer, radiation dryer and high frequency electric field dryer. Among them, conduction drying dryer was widely used by grain enterprises in 1980s and early 1990s. This dryer is also called steam boiler, granary, preheating tower, drying tower, cooling tower and various conveying equipment. It has the advantages of large precipitation, 10% - 15% water reduction at a time, large production capacity and high degree of automation. Its disadvantages are high cost, high fuel consumption and inconvenient maintenance.

The working principle of the dryer is as follows:

Flow chart of grain drying

In this drying method, the steam does not directly contact with the grain, but passes through the metal pipe. The grain flows outside the pipe to absorb heat. After being heated, the temperature of the grain rises and the moisture inside it is transferred. The water is evaporated from the surface and taken away by the drying medium, thus reducing the grain water content.

According to its working principle, the consumption reduction methods are as follows:

1. Improve the drying medium. When grain is dried, the material that can be mixed with steam and taken away is called drying medium. According to the definition of drying medium, if the drying medium can heat the grain in the drying process to a large extent, and take away the vaporized steam, then the grain can be dried. This depends on the capacity of the drying medium to water vapor, that is, the humidity of the air. The humidity of air at different temperatures is different. At a certain temperature, the amount of water vapor contained in the moist air has a certain limit. When the quantity of water vapor in the atmosphere reaches a dynamic balance with the amount of water vapor condensed into water in the air, the amount of water vapor contained in the air reaches the maximum limit. At this time, the air is called saturated air, and its humidity is called saturated humidity. The saturated humidity of the same kind of air is different at different humidity, such as 17.2g/m3 at 20 ℃ and 37.3 g / m3 at 34 ℃. It can be seen that the higher the saturation humidity value, the stronger the drying ability.

In the traditional steam dryer, the flue gas is put into the steam after passing through the pre heating tower, which not only pollutes the environment, but also wastes heat energy. In order to improve the utilization effect of heat energy, flue gas can be directly used as drying medium. The specific transformation method is to direct the flue gas into the heating tower through the flue gas box after preheating. In this way, the temperature of drying medium can not be increased effectively. It should be noted that the temperature of furnace gas should be paid attention to during production. If the temperature is too high, the quality of grain will be affected. Generally, the temperature of drying medium should be controlled between 80 ℃ and 130 ℃.

2. Drying ventilation drying method was used. In the traditional drying method, grain is usually dried to moisture content of 14% - 15%, and then cooled and stored. And the drying ventilation drying method first carries on the high temperature drying to the grain. The moisture content of grain is reduced to 18%, and then the grain with the moisture content is sent to the warehouse for 5-7 hours, so that the temperature and moisture between the grain interior and surface tend to balance, and then the slow ventilation is carried out, the air volume is 25 m3-50 m3 / h, and the ventilation time is about 8 hours, so that the temperature of the grain is the same as that of the atmosphere. 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) increasing the drying amount. (2) reduce energy consumption. Because the precipitation rate of grain in the equipment is low; in the process of slow cooling, the heat energy accumulated by grain itself is used to further precipitation. (3) Ensure the quality of grain. Because the direct cooling of dried grain often results in grain burst, and the application of this method can reduce the waist burst rate and breakage rate; (4) the drying cost can be reduced by about 13%.