Recently, China's first batch of overhead grain air film silos successfully completed the work of loading grain silos and officially put into use. 30,000 tons of soybeans became its first residents. With a diameter of 23 meters and a height of more than 36 meters, one capsule can store 7,500 tons of grain, which can meet the annual food supply of 70,000 people.
The gas envelope is not just a big balloon. Its outermost layer is a gas film layer, which can play a very good airtight and waterproof performance. There is also a thick layer of insulation in the middle. The most internal is the reinforced concrete structure, which can play a strong supporting role.
At the top of the gas film bin, when the temperature outside the bin is about 30 ° C, the temperature inside the bin is about 22 ° C. The temperature difference between inside and outside the warehouse is about 8 ° C, and the insulation performance is very obvious.
From the top of the silo into the interior of the silo, you can see from the profile model of the silo that this represents 23 meters of grain pile, and I am standing on this position on its surface. Down from where I was standing, there was a 23-meter pile of grain. We see that there are 25 blue multifunctional cables evenly distributed throughout the granary, and there are 14 sensors evenly distributed on each cable, so there are 350 in the entire granary. These cables run deep into the bottom of the grain pile, ensuring that all grain is always in the optimal storage environment.
At present, the mainstream storage silos in the grain industry are tall bungalow silos, shallow round silos and so on. Grain air film silos are obviously superior to these traditional silos in terms of thermal insulation and airtight performance. Grain is stored in the air film bin, which can achieve the effect of quality preservation and loss. After the grain is stored in the air film bin for a complete cycle, the quality of the grain will be significantly better than that of the grain in the traditional storage bin. If the traditional grain storage method is compared to wearing an ordinary cotton coat to the grain, then the air film warehouse is like changing it to a high-grade down jacket, and its performance will be significantly improved.
How is the gas film silo built?
The first step is to build the foundation and pour the overhead platform of the air film bin to bear the load of the grain and the bin itself. The second step is to spread the film and blow the film, the film material is rolled out and continues to drum air into the film, 1 mm thick, weighing more than 4 tons of polymer film material will be blown up like a balloon, which is the outermost layer of food gas film silo. As the 5th generation of building materials, membrane material has the advantages of waterproof, moisture-proof and sunlight reflection. Next, the construction personnel will spray the insulation layer of the warehouse body inside the membrane material; The last step is to carry out the construction of the reinforced concrete structure layer. After the reinforcement is bundled, the concrete injection is carried out. The structure of this layer will effectively withstand the huge side pressure exerted by the grain pile on the vertical silo wall.
After the outer membrane is aerated and formed, the entire construction process is carried out in the membrane, and the construction process is highly mechanized, safe and environmentally friendly, and almost unaffected by the environment and weather. Once the gas film warehouse is built, let's look at the warehousing process.
The grain is transported to the warehouse through the container, and after quality testing and weighing, the vehicle will be unloaded to the designated grain unloading area. With the box slowly lifted, the grain flow into the underground grain discharge pit, and after the first lift to remove impurities, after the grain will be lifted for a second time, through the closed conveyor equipment into the lifting tower, the food will be lifted to the top of the air film bin more than 30 meters high.
The distributor installed on the top of the warehouse can make the soybean fall evenly and dispersed when it is put into the warehouse, reduce the automatic classification of grain and the accumulation of impurities, and is more conducive to the subsequent safe storage.
In the process of loading grain, due to the grain flow and other reasons will form a number of cone grain surface in the warehouse, the uneven grain surface will increase the difficulty of safe storage in the later period, so after the warehouse is filled, the custodian will carry out the grain surface leveling work in time to achieve the standard of "flat as a mirror", and prepare for the next storage process application such as ventilation and cooling.
The technology of the gas film bin for storing grain is actually derived from the innovation of coal storage. Its outermost white film layer can play a very good reflection of sunlight and waterproof performance. After aeration molding, a yellow foam insulation layer is sprayed on the inside of the film layer, which can play a very good thermal insulation role. The grey reinforced concrete layer in the innermost part eliminates the need for scaffolding during the entire construction process. Moreover, it is not affected by weather factors such as wind, rain and snow, and the entire construction process is fast and convenient.
Although the technology for building grain gas silos is derived from the innovative technology of coal storage warehouses, it is still very different from the items stored in coal warehouses. Compared with the coal bin, the grain gas film bin is much higher in terms of thermal insulation performance, airtight performance, and waterproof and moisture-proof performance. After all, food is to be eaten in the mouth, and the safety of food must be fully guaranteed. In the research and development process from coal bunker to grain gas film bin, the team has broken through more than 20 technologies, made a world first, and achieved a major technological innovation in the field of green grain storage in grain storage bin.
Gas film granary advantage
Excellent thermal insulation, air tightness and water resistance
The outer layer of the grain gas film warehouse is covered by PVDF film material as a whole, and the construction is integrated and formed, with excellent thermal insulation, air tightness and water resistance.
The measured results show that the heat transfer coefficient of the film chamber is 0.4403W/m2/K, which is much lower than that of the shallow chamber 1.4782W/m2/K. The half-life of 500Pa air tight pressure of the gas film bin is 4312 seconds, far exceeding the 300 seconds design requirements of the grain bin; Lined with polyurethane foam, the thermal conductivity is only ≤0.024w/m.k), far less than the concrete thermal conductivity of 1.74w/ (m.k), good thermal insulation effect.
The top of the warehouse is shaped as a dome, no rainwater collection, long-term reliable waterproof effect; The experiment shows that the grain temperature in the bin does not change with the change of the temperature of the bin wall, the internal basically constant temperature and humidity, low temperature grain storage is easier to achieve, and the grain storage quality is good.
The construction mechanization degree is high, the construction period is short; The main construction is mainly carried out in the inflatable film, which is little affected by external environment and weather factors, and can realize all-weather interference free construction, environmental protection and efficiency. The index of grain area per ton of gas film bin is much smaller than that of cottage bin, which can effectively improve the grain storage rate.
Low operation and maintenance cost
Because its air tightness is greatly improved, low temperature equipment configuration costs are reduced, ventilation time is reduced, warehouse operation and maintenance costs are greatly reduced, and the whole life cycle operation and maintenance costs can be saved by more than 30%. A gas control pest control cycle, only need to supplement high purity nitrogen once within 28 days, greatly saving the operation energy consumption; The external membrane has a self-cleaning function, which reduces the maintenance cost in the later period. In line with the requirements of the "double carbon" strategy, it has a milestone significance of extending from green grain storage to green warehouse.
The ventilation design in the warehouse is more scientific and reasonable, the flame retardant level reaches B1 level, and the fire safety capability is greatly improved.
The main body of the granary adopts the gas film + reinforced concrete thin shell structure, namely the gas film reinforced concrete structure, which consists of PVDF membrane material, polyurethane foam layer and reinforced concrete structure layer from the outside to the inside. The warehouse body is integrated and formed, with excellent waterproof, heat preservation, heat insulation, airtight, moisture-proof and other properties, which can better meet the requirements of grain storage. And using the patented technology, for the first time in the gas film reinforced concrete storage bin using the bottom of the overhead technology, to realize the mechanization of grain out of the warehouse.
The roof of the traditional gas-film reinforced concrete storage bin is a hemispherical dome, and the three-center spherical vault structure is adopted for the first time in this project, which makes the radial ratio of the dome change from the traditional 0.5:1 to 0.35:1, thus reducing the invalid space by 1/3 and greatly reducing the operation energy consumption. Moreover, its dome structure has good mechanical properties, can adapt to large loads, has strong earthquake resistance and wind resistance, and its mechanical properties are better than shallow silo cone top structure.
The research and development team cooperated with universities, on the one hand, the theory was simulated on the software, and through research, the theoretical model was formed which was accurate, simple and practical and in line with the reality. On the one hand, three small "experimental silos" were established to carry out simulation experiments. Through testing and comparison, many parameters required for the construction of gas film granaries were obtained. The traditional crane construction is replaced by the construction method of independently developed hydraulic jacking combined work platform, which effectively avoids the problems such as difficult maintenance of the crane in the thin and tall air film silo, repeated moving of the car construction, and tail gas treatment in the confined space, which improves the work efficiency, improves the safety performance, and reduces the construction cost.
On July 15, the China Society of Grain and Oil organized a scientific and technological achievements evaluation meeting in Chengdu, and the "Special pilot research project on grain gas film reinforced concrete dome facilities and equipment" successfully passed the scientific and technological achievements evaluation. It shows that the design and construction technology of the project has reached the international advanced level, and the index of air tightness and thermal insulation is leading in the world.
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