Permanent Grain Storage

From the dawn of civilization and humankind’s earliest efforts at mass agriculture over 10,000 years ago, little has changed in the challenges associated with grain storage. Efforts to seal and protect grain stores against losses to spoilage and pests have led to countless approaches to grain storage systems. In Spring Grove, Illinois in the Spring of 1873 the construction of what may have been the first above ground silo, was seen as a large departure from the bunker and pit storage techniques that continued to prove impossible to seal against the elements and biological processes that lead to spoilage. In the 1970’s and 80’s technologically advanced polymers were becoming commercially viable. These materials were resistant to ultraviolet degradation from sunlight, had a very high tensile strength and blocked the transmission of both light and gasses. These durable and lightweight materials facilitated the development of grain bagging as the most dramatic technological change in the approach to grain storage systems.

Prehistoric subsistence farming and grain storage has given way to globalization, warehousing and the agricultural apparatus required to feed a burgeoning global population. The trends toward farm amalgamation and the sprawling growth of high-efficiency farming operations polarizes the grain storage needs of the newly settled villages of 4000 - 2000 BC. Despite many advances in grain storage construction techniques, the challenges have remained the same while the need for flexible on-site grain storage continues to increase.

Regardless of the duration of storage, be it weeks, months or years, grain stores are continually in flux and subject to continual degradation and spoilage. From the natural metabolic processes within the grain itself, the elements of wind, rain and heat, birds, rodents, insects and micro-organisms continue to inflict spoilage losses estimated in the billions of dollars each year.

In the past century, advances in new construction materials and methodology have reduced spoilage. Average losses of 40% or higher in some cases have been reduced to 15-25% with the use of improved permanent storage structures. Grain silos of reinforced concrete for example, provide superior protection from the elements and outlast their wooden counterparts. Although they are not hermetically sealed, they are also not breathable structures and therefore do not allow for the exchange of gasses or release of moisture. For these reasons they generally require forced aeration or carbon dioxide infusion techniques to control heat, moisture and pests. They are also cost prohibitive in most farming operations.

Wooden grain bins and silos are a much more affordable grain storage structure and allow for breathability, but offer less protection from the infiltration of external moisture and pests. They also require a high level of maintenance and deteriorate over time.

Steel bins are the most common permanent grain storage structure, but also require a very  significant capital investment of as much as $4 per bushel of storage capacity. Like their reinforced concrete counterparts, these structures are not hermetically sealed and can often require costly aeration techniques to mitigate their biggest downfall—convective heating due to the very high thermal conductivity of metal. This often leads to moisture migration and areas of high microbial activity and grain deterioration.

The one commonality between all of these permanent structures is that they are not hermetically sealed and require augmentation techniques to mitigate spoilage. Attempts to create controlled-atmosphere environments within these structures using flexible polyurethane, acrylic and elastic sealants have been met with limited or temporary success and longevity.

Grain Bagging for Hermetically Sealed Grain Storage

All of the biological processes involved in the degradation of grain quality and spoilage require oxygen, moisture and heat. In traditional grain storage bins, the approach to arresting these damaging biological processes is to remove moisture and heat through forced aeration and sterilization by infusing the contents of the bin with carbon dioxide. These processes are costly and require that the bin not be hermetically sealed in order to accommodate the flow of aeration and gases.

Grain bagging creates a hermetically sealed storage enclosure, eliminating all exchanges of gas with outside atmosphere. In a sealed environment, the natural lifecycle degradation of a grain’s cellular structure as well as that of microbial growth, is a process of aspiration that is inhibited in a low-oxygen environment. When grains with a relatively high moisture content—or what would be considered high for traditional grain storage—are hermetically sealed in a grain bag, the biological processes within the bag quickly consume the very limited supply of oxygen and begin to self-sterilize though the release and build up of carbon dioxide, toxic to microbial growth. This low oxygen, high carbon dioxide environment naturally controls pests and microbial growth.

The Effects of Heat on Grain Storage

Heat speeds insect and microbial growth and increases the breakdown of carbohydrates, proteins and sugars within the grain. A natural byproduct of this process is the release of even more heat and moisture.

Traditional grain storage bins are subject to a high amount of convective solar heating. This is particularly prevalent in metal bins. Their large inner volume allows for the core of the grain store to remain cool, which maintains a large temperature gradient at all times. The convective outer heating creates a process know as “moisture migration”. In this process, the outer areas of the bin heats the grain and surrounding interstitial air. This heating process lowers the moisture retaining capacity and forces the moisture out of these hot spots and into contact with the cooler inner core and top exposed surface area. This moisture is then rapidly cooled to the dew point, and condenses forming  highly saturated areas of grain where microbial growth and further breakdown of the grain’s internal structure occurs. As perviously mentioned, this process releases both additional heat and moisture causing these areas to rapidly deteriorate. Further to this, in a traditional grain bin, condensation is formed through the natural heating and cooling of the open air parcel at the top of the bin introducing further moisture and spoilage that is not present in the grain bag enclosure.

With grain-bagging, the inner core of the stored grain has substantially less mass, even with bags as wide as 12’. This allows the grain to more easily achieve temperature and moisture equilibrium. Due to the lack of atmosphere-exposed grain surfaces within the bag, the effects of condensation are reduced or eliminated. The large surface area of the grain bag allows ground cooling to mitigate the accumulation of heat. The white polyurethane material has low thermal conductivity properties and it’s above ground surface area provides excellent air-cooling properties.

The same structural qualities that allow for excellent temperature regulation also provide grain bags with a very low centre of gravity and very low aerodynamic drag, providing a great deal of wind resilience in extreme weather conditions.

Grain Bagging Capital Costs and Operational Flexibility

The cost of transporting grain to permanent grain storage structures can be very significant, particularly for agricultural operations that span great distances. Unlike permanent grain storage structures, for the first time, grain bagging allows the structures to be erected at or near the point of production. From the operational costs of trucking alone, the gains in efficiency of this practice can in many cases offset the capital costs of the required equipment in a very short period of time.

With average costs for grain bagging well below $2 per bushel including depreciating the equipment value to $0 over 10 years, and spoilage reduced to well under 10% even for durations of two years in some cases, the flexibility and cost-benefit of grain bagging is clear.

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