Storage silos are structures for storing bulk materials. Silos are used in agriculture to store grain (see grain elevators) or fermented feed known as silage. Silos are more commonly used for bulk storage of grain, coal, cement, carbon black, wood chips and sawdust. Three types of silos are in widespread use today:
- Tower silos
- Bunker silos
- Bag silos
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Tower silos
Storage silos are cylindrical structures, typically 10 to 90 ft (4 to 30 m) in diameter and 30 to 275 ft (10 to 84 m) in height with the slipform and Jumpform concrete silos being the larger diameter and taller silos. They can be made of many materials. Wood staves, concrete staves, cast concrete, and steel panels have all been used, and have varying cost, durability, and airtightness tradeoffs. Silos storing grain, cement and woodchips are typically unloaded with air slides or augers. Silos can be unloaded into rail cars, trucks or conveyors. Tower silos containing silage are usually unloaded from the top of the pile, originally by hand using a pitchfork, in modern times using mechanical unloaders. Bottom silo unloaders are utilized at times but have problems with difficulty of repair. An advantage of tower silos is that the silage tends to pack well due to its own weight, except in the top few feet. The tower silo was invented by Franklin Hiram King. In Australia, many country towns in grain-growing areas have concrete tower silos to collect grain from the surrounding towns and store it ready for transport by train or road to an export port.
Bunker silos
Bunker silos are trenches, usually with concrete walls, that are filled and packed with tractors and loaders. The filled trench is covered with a plastic tarp to make it airtight. These silos are usually unloaded with a tractor and loader. They are inexpensive and especially well suited to very large operations.
Bag silos
Bag silos are heavyweight plastic bags, usually around 8 to 12 ft in diameter, and of variable length as required for the amount of material to be stored. They are packed using a machine made for the purpose, and sealed on both ends. They are unloaded using a tractor and loader or skid-steer loader. The bag is discarded in sections as it is torn off. Bag silos require little capital investment. They can be used as a temporary measure when growth or harvest conditions require more space, though some farms use them every year.
Safety and silo cleaning
Silos are hazardous, and people die every year in the process of filling and maintaining them. The machinery used is dangerous and with tower silos workers can fall from the silo's ladder or work platform. There have also been many cases of silos exploding. If the air inside becomes laden with finely granulated particles, such as grain dust, a spark can trigger an explosion powerful enough to blow a concrete silo apart. There are two main problems which will necessitate cleaning. Bridging occurs when the material consolidates at the base of the silo. Rat holing occurs when the material starts to adhere to the side of the silo. This will reduce the operating capacity of a silo as well as leading to cross-contamination of newer material with older material. There are a number of ways to clean a silo and many of these carry their own risks. However since the early 1990s acoustic cleaners have become available. These are non-invasive, have minimum risk, and can offer a very cost-effective way to keep a silo clean. It can also be called silage wrap.
Notable silos
- Schapfen-Mill-Tower, Ulm, Germany, height: 130 metres
- Henninger Turm, Frankfurt, Germany, has an observation deck and 2 revolving restaurants, height: 120 metres
- Silo Tower Basel, Basel, Switzerland, has an observation deck, height: 52 metres
- Quaker Square, Akron, Ohio, is a former set of tower silos that is now a hotel, restaurants and shops
References
- Beedle, Peggy Lee. 4. "Silos: an agricultural success story", University of Wisconsin-Extension: 2001, G3660-4.
See also
External links
- International Silo Association
- Machine for silos cleaning
- FRAME Grain Storage Metallic Silos (courtesy of FRAME SpA, Italy)
- What To Do In Case Of Grain Bin Entrapment, from the U.S. National Agricultural Safety Database
- The Powder and Bulk Channel - Solutions for the Powder and Bulk Industry
- Demonstration of Grain Silo Explosion at WonderHowTo.com
