MEET THE SILOs : The "Lords" of Agricultural Storage explained.

Welcome once again to my blog, it is both a joy and an esteemed privilege to have you here.

Recently, I have delved into two major alternative ways of planting. These of course were invented to improve agriculture, and truly they have and are still playing their part as Geoponics still continue to play a major role in Agricultural production.

There have also been several machineries to enhance the mechanization of all agricultural processes, and evidently, these too have played a very great role in improving agriculture. But for all of these, there is a part of agriculture that is also a major shareholder in ensuring the success of the whole process- Storage.

Yes, agricultural products are biological materials which means that they have a tendency to degrade because they respire, also they react with their environment (hygroscopy being an example of this). Also humans are not the only species that agricultural products serve as food for, which is why they are also under the constant threat of pests and disease attack.

To prevent products from all these and still maintain their qualities is a very important process in agriculture that can not be overlooked. So important it is that a branch of Agricultural Engineering is dedicated to it (that branch is in fact my specialisation - Crop processing and Storage). Today, however, we are not here to talk about Storage as a whole, that will be for another time. We shall be talking about one of the most widely used Storage structures.

A lot of storage structures have been used for agricultural products, ranging from Cribs to Warehouses,barns, to Rhumbuses and Silos etc. But, recently I've had to answer many questions about one of these structures from those that know I studied Agricultural Engineering.

However, as an Engineer, I was trained to maximise efficiency, so in a bid to avoid repeating myself everytime a new person asks those questions or having to talk on and on, I've decided to write this post and includethe basic details people may care to know about the structure in question.

You must have seen this particular structure yourself, and you've probably been nursing some questions about it too. It is easily found at food processing factories, standing like a tower and mostly cylindrical in shape (although there are other shapes). You probably spotted the ladders by its side and the trough-like structures above it. If you haven't guessed it yet, I'm describing the Silo.

Certainly, if there is a throne for the ruler of storage structures, the Silo will comfortably sit atop it with a shining crown. Well, today we shall discuss how they came to be of such importance, what they offer in terms of storage, how they do the storage job, the different types available (this is usually at the center of most questions I've received), If and how they can fail us. Shall we get started? ..I'll take that as a YES.
So, then

MEET THE SILO
Were you to check for the definition of Silo online, you will hardly find one single definition that totally holds true to what a Silo is. This definition by the Cambridge Dictionary though, is the closest I found. It defined the Silo as

a big structure that usually has the shape of a cylinder, that is used for grain storage or for storing winter food for animals.

Like I said, it's a close description, aside from the fact that it didn't mention that Silos are used for storing other things in powdery form and that their contents are used for more than animal feeding, it has said most of what is required. They are also used for storing Silage (when I was younger, I actually thought, the name "Silo" was because it stored Silage, don't laugh at me, I was just a boy trying to understand the world), cement, sawdust, coal etc.

If you've passed by breweries before or you've seen a picture of breweries, you must have seen something that looks like the picture on the right. Silos are used in such processing factories or on farms to hold grains and other materials, before and during the processing process.

They are classified among Large scale storage structures (structures that can store above 100 tonnes) as they can store as much as 800 tonnes of products. This usually means that they require extra care from experts for their installation and operation. As also mentioned, they come in other shapes apart from the common cylindrical types and can sometimes be underground.

Apart from the more common cylindrical shape, they also come in rectangular or hexagonal shapes. Their bottoms are either flat or Conical in the form of an hopper.

How do they store products
As large as Silos can be and as much capacity they can have for storage, there is one thing they certainly do not possess -Magical powers. They are instead simple and humble structures that hold your products for you until you are ready to take them. Yes, they hold them for you.

Did you know?
The process of storing materials in Silos is called Siloing

If you remember though, I mentioned some of the characteristics of Biological materials being hygroscopic and susceptibility to degradation. For this reason products like grains stored in Silos will be as good as spoilt when you go to retrieve them if efforts are not made to control them while in storage.

However, research works have shown that keeping products at their Equilibrium Moisture Content (EMC) with a corresponding temperature and proper relative humidity ensures longer shelf life of the products. For this reason, Silos are designed to determine and maintain these conditions in various ways, and this is the basis for the first classification of Silos we shall be discussing today. Under this category, we have the Conventional Silo, Instrumentalised Silo and the Computerized or Automated Silo.

The Conventional Silos are those that follow the age old method of manually checking the conditions(temperature,moisture content and Relative humidity, pressure) in the Silo. This is sometimes done by sampling the products taken from the Silo. A problem, however is that due to the large size of Silos, it is usually very hard and tedious to properly determine the conditions. Once the conditions are established, proper adjustments( e. g aeration) are manually or mechanically made to maintain an ambience conducive for the preservation of the product. This types though, are not totally safe, as farmers have faced hazards while measuring, sometimes even resulting in death.

As for Instrumentalised Silos, they go a step further in that they have various measuring devices installed with the Silo to determine those conditions, for example, having a pressure gauge installed to determine the pressure. Here, all the farmer has to do is to read measurements and make necessary adjustments. It becomes easier than the conventional method because the drudgery and time consumption is drastically reduced, and measurements are more accurate.

If you're beginning to love the method just explained, then you'll love the Computerized or Automated Silos even more. These Silos have various sensors installed in the system to automatically measure the conditions and then feed this to a computerized system that can sense what conditions need to be adjusted, and triggers the process without any human control.

For example, if the temperature sensor, sends information about too high temperature, the system triggers the humidifier immediately. They are also designed to sense local temperatures in the Silo and in this case they trigger the rotation if the Auger to ensure uniform temperature. The ability of this system to successfully work with little or no human supervision is the reason it has become the rave of the moment.

Now, that's done. As you might have noticed above though, there has been constant mention of aeration. The reason is because the supply of air, the kind of air supplied or total abstinence from air in the Silo form different ways of preserving the shelf life of products stored in the Silo. So the type of aeration a Silo uses is another major criterion for classifying them, the types here include : Mechanically Ventilated Silo, Hermetic Silo, Gas Silo and the Controlled Atmosphere Silo.

Owing to the name, Mechanically Ventilated Silos get their air from mechanical means like fans or blowers that supply air into the Silo. As for the Hermetic Silos, they preserve the agricultural products by ensuring that the Silo is airtight, thus ensuring that biological activity is eliminated in storage. It has turned out to be an effective way of keeping pests at bay and preserving the quality of the products.

Gas Silos in their own case, preserve agricultural products stored in the Silo by introducing certain gases like Nitrogen and Oxygen at certain levels to maintain certain properties of the stored materials. For example, Low-oxygen Silos are used to prevent decay and mold, and to also preserve the quality of fermented products stored in them.

When we speak of Controlled Atmosphere Silos though, you may easily draw a parallel with the Computerized Silos explained above. Everything here ranging from the temperature to the relative humidity to the EMC, to the oxygen and nitrogen levels are monitored by sensors and regulated to be at the exact atmospheric conditions needed at every point in time, irrespective of the atmospheric conditions obtainable in the surroundings of the Silo. With this kind of system, you could create a winter-like atmosphere inside your Silo when you're actually in Summer.

Now we move to another basis for classifying Silos, which is by the materials from which they are constructed. In this case you have the Metal Silos which may be made from Aluminium or Steel, Concrete Silos, Wooden Silos, Mud Silos and Composite Silos which are made from materials formed from a combination of two or more of the materials earlier mentioned to achieve a superior property in the new material which enhances the Silo's quality.

A final basis for classification of Silos, which you will usually hear from the Engineers is the classification based on how structurally stable the Silo is. You either describe them as Deep Silos or Shallow Silos.

To make this less complicated, let's put it this way, if you find a Silo whose smallest lateral dimension is larger than the depth, then you have yourself a Shallow Silo. However, when a Silo's depth is larger than the smallest lateral dimension, then what you have is a Deep Silo. They can also be described in terms of the rupture plane, but strictly in the spirit of not wanting to complicate the explanation with a description that might look like Alien language (unless you're very good with planes and solid mechanics), I'll have to refer those really interested in knowing more about that to check here.

When Silos Fail
As useful and as helpful as Silos are, when they fail, it is usually catastrophic. Literally, people die when Silos collapse (Lewis 2006), not everytime of course. What is sure everytime, however is the loss of materials which can sometimes be as much as thousands of tons, the materials that are not lost can get contaminated. Remember too, that the Silo, no matter how expensively constructed will be lost by then too.

When Silos fail too, they sometimes fall on other structures, either other neighbouring Silos or other structures on the same farm, leading to an even greater loss for the farmer. I remember one of my Professors mentioning that he knew about a farmer that committed suicide after his Silos failed, these kind of sad experiences happen because a lot of investments have been made into the Silo itself and the products it is storing.

Another person that may suffer from the failure of a Silo is the engineer that carried out the construction of the Silo. Of course he may not be present when the failure occurs, but he may face litigation for the failure if his work.

These failures can occur in the form of explosion which are usually caused by the building up if gases in the Silo, mainly in the case of Silos used for storing Silage, although some grain Silos have been reported to have exploded.

Please, here is a friendly warning : if you ever find yourself inside a Silo, try to avoid causing any sparks or lighting any fire.

Failure can also occur through dents in the Silo, buckling of the Silo or total outright collapse of the structure. These are due to numerous factors, most of which have to do with the forces or loads that the Silo encounters. These can be wind load (since Silos can be tall), axial stresses experienced at the base of the Silo due to the Silo's own weight and that if the material it is storing. The properties of the Soil upon which a Silo's foundation is laid also plays a major role in its survival or failure.

Load exerted on the Silo by the stored materials is one of the most complicated reasons for failure, since different materials have different load characteristics.

Thankfully, though, an important technique in engineering is redundancy, and how it comes to play in Silo storage is this. Suppose you have 95 tons of products to store, and you have a Silo that has 100 ton capacity, do you just load it all in that Silo? NO, that will not be a very good choice, in fact engineers are taught not to. It will be a better to choice to equally divide the products into two Silos of 100 ton capacity, so that you reduce the load that the Silos have to withstand, and in the unlikely event that one of them eventually fails, you still have at least half of your products safe.

In fact, it is interesting to note that some large processing companies, have much more Silos than they can need at a time, to ensure reduction in load, and allow for movement of materials if there is any need for Silo maintenance or even failure-enforced transfer. This practice may look like an unnecessary waste of resources until failure occurs, and you realise that the cost of the excess Silos are nothing compared to the great losses that come with Silo failure.

How are they designed
Due to the high cost and technicalities involved in the construction of Silos, they are best left to the Engineers who have been trained to do so. But, then let me give you a hint as to what the Engineers have in mind when designing a Silo.

• Required Capacity : Before designing a Silo, there is need to know how much of that farm's produce or how much of processing raw materials will be stored it. This information will guide capacity and number of the Silos to be designed, to ensure efficiency, safety and flexibility for future expansions.

• Silo Location : You will agree with me that there is no point spending large sums of money to make Silos if they will not be efficient. For this reason, engineers who design Silos ensure that it is located on the part of the farm that brings about ease of movement of materials in and out of the Silo, also close to the source of power. However, they locate it at a reasonable distance away from residential buildings on the farm.

In processing factories, Silos for storing raw materials are located at a position that is accessible for transportation so as to easily receive the materials, at the same time as close as possible to where the materials will be processed. Silos are better helped when located on Soils with high load bearing capacity and away from flood prone areas.

• Handling Equipment : The choice of handling equipment( e. g conveyors) to be used for the loading and unloading of the Silo, including the method to be employed is a great factor in designing Silos.

• Structural Stability of the Silo : This is the analytical part of the design process where the designer takes into account all the possible forces that can affect the Silo and ensures that the structure can withstand them. This is what also informs his choice of either a Deep or Shallow Silo.

Did you know?
One of the reasons why cylindrical Silos are more predominantly used is because they are free from corner effects that plague rectangular and hexagonal Silos.

CONCLUSION
Silos have been in use for a very large part of the human story dating as far back as the B. C era, they play a very important part in our everyday life by preserving most of the grains that form part of our staple everyday (something tells me you've directly or indirectly taken a grain product today... thank you, I know I'm right) irrespective of their shape or size, and when properly handled they have proven to be very great partners in the advancement of Agriculture.

However, due to the height of Silos and the volume of materials they usually handle, it is almost impossible and not exactly hygienic or efficient to manually move the materials to and from the Silo. So, what comes to the rescue in handling materials stored in Silos or other large storage structures. Please be here next week as I shed light on this aspect of Storage and Processing.

Thank you for reading, I hope it was worth your while.

REFERENCES

• Adem D., Zeki K., Ahmet D., Halil S. (M. ASCE).(2009).Cause of Damage and Failures in Silo Structures. JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES ASCE. MARCH/APRIL 2009. pm 65-71.

• Adewumi, B.A and O.S.V Oduwole. (1995). Problems affecting the utilization of silo storage in Nigeria” NSE Technical Transactions 3 (2): 27-32.

• Babarinsa, F.A. (2001). Grain storage in silos without insecticides. Post Harvest News 3:1-5.

• Brummer , H. (1989). Grain cooling in steel silo. World Farming 8:30-35, 1983.

• Dwayne R. Buxton. (2003). Silage science and technology, American Society of Agronomy, Inc., 2003, p.1

• Faseyi, O.W. (2001). Report on the training organized by the Chinese Government on grain storage management and technology. Federal
  Ministry of Agriculture, Nigeria. 20pp.

• Graham, J. (2011). "Drowned in corn: Grain bin deaths hit record". Chicago Tribune.

• Igbeka, J.C. (1991). Indigenous and modern methods of grain preservation and storage. An invited paper presented at the NSE course on design, construction and maintenance of food storage system.

• Lewis, J. 2006. “Silo failures—Why do they happen? February 13, 2006.” (http://www.powderandbulk.com/blog/archives/2006/02/)

• Lost Farms of McHenry County. Arcadia Publishing.

• Sinha, R.N &Muir. Grain Storage: Part of a System. Avi Publisher.

• Sinha, R.N 1971. Interrelations of physical , chemical and biological variables in deterioration of stored grains. In: Grain storage Part of the system.

SILO | BULK STORAGE | GRAIN SILOS

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