How Does A Grain Silo Operate?
How Does A Grain Silo Operate?
Apart from the storage of grain, a grain silo provides various services to grain farmers and forms an integral part of the agricultural value chain. It uses technical engineering and operating skills in a competitive environment and depends on specialized, capital-intensive facilities. Grain silos use these facilities to dry, clean, grade and blend whole grain.
Grain is moved in bulk throughout the handling and storage system. It is transferred from place to place without a container. In most cases, the ownership of, or at least the responsibility for, the grain changes hands when it enters or is discharged from the grain silo. This means that the silo must be equipped to measure accurately the quantities and qualities of the grain entering and leaving the facility. Special equipment is used to facilitate accurate weighing, sampling and testing of grain in silos. The mechanical transport of grain within the silo is done by means of specialized conveyer belts and elevating equipment.
The method for harvesting maize has shifted over the years from ear maize harvest (at moisture levels safe for storage) to harvesting with combines, where the standing ear maize is converted mechanically directly to shelled maize at moisture levels that are often too high for safe storage. Although rapid harvest at high moisture levels reduces field losses, it increases the damage to kernels and the possibility of spoilage. The higher moisture levels at which maize and other grains are often harvested result in a product that is not safe for immediate storage. Rapid drying is therefore essential to prevent fermentation as well as fungal and insect infestations. Drying also eliminates water that must otherwise be transported and thus drying is usually performed at the earliest possible point in the grain handling system.
Grain silos provide drying services for farmers. A drying system comprises several components, namely the dryer itself, the control system, the fuel system, handling equipment to empty and fill the dryer, and also sufficient grain holding capacity for wet grain.
Aeration is the movement of small amounts of air through a stored grain mass to prevent deterioration of the grain due to fungi and insects. Aeration keeps the grain at a uniform cool temperature and also removes small amounts of moisture from the grain. Higher, uneven temperatures cause moisture movement and condensation within the stored grain that stimulates fungal growth and insects. Neither fungi nor insects, however, will thrive at the lower temperatures.
Cleaning is used to separate or "screen" out foreign matter and cracked kernels from whole, dried grain. A by-product of cleaning operations on maize is maize screenings. Screenings are sold to feed lots and are occasionally mixed back into the outloaded grain. The average level of foreign material in a grain lot can be controlled more precisely by blending pure screenings into clean grain than by mixing several streams of grain with varying foreign material content. The cleaning system for a grain silo involves several components, including the cleaning machines themselves, the control system, handling equipment to deliver grain to and from the cleaning system, and several special bins for the unclean grain, the cleaned grain, and the screenings which are the by-products of the cleaning process. Dust control systems and dust holding bins are also required to prevent the hazard of dust explosions during the cleaning process. Similarly, the fumigation system for a grain silo involves several components, including the fumigation application equipment itself, the bins in which the fumigation is to take place, and air circulation equipment. All fumigants, whether liquid, gas, or solid pellets, change to gas and are only effective when the proper mixture of gas and air is maintained within the bin for an extended period of time. Thus, the bins in which fumigation is to take place must be sealed so as to be relatively gas tight. Fumigation involves the handling of toxic substances. It represents a serious safety hazard and therefore strict precautionary measures have to be followed.
Several lots of grain are blended in order to standardize the grain so that it will be uniform and meet grading standards as well as customer specifications. Blending can change the moisture content, density, hectoliter mass (test weight), and overall physical characteristics of a particular grain lot.
It can also change functional characteristics, such as oil content and protein levels, of the grain lot. By mixing diverse lots of grain, the silo operator attempts to prepare large lot of grain with uniform characteristics that represent the average of the combined lots. Blending, however, is much more than the simple combining of two grain lots to reach an average. The uniformity of the larger lot is not assured to be better than the individual components because segregation may occur.
Blending requires sophisticated equipment to control flow rates and to collect samples for monitoring purposes. Grains with different quality levels or specific quality factors are stored in separate bins. Blending is accomplished by drawing a grain type (e.g. maize) with different qualities from the various bins into a collecting bin.
For each grain type there are several individual quality parameters that are used collectively to establish the numeric grade of grain. The numeric grade of a given lot of grain is set by the level of the worst factor. The silo issues an official quality/grade note per load based on these standards when the grain is delivered as well as during dispatch.