Storage in bags
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This method consists of conserving dried and cleaned grain in bags made of plant fibre or plastic, and neatly stacking the bags in carefully prepared areas.
This method is little used in developed countries but is widespread in developing countries. It is economical and well-adapted to local grain-transport and marketing conditions.
There are several ways of storing grain in bags. The bags of grain can be stacked out-of-doors under tarpaulins, or placed inside storehouses, sheds or warehouses.
Sometimes, especially for seeds, grain is stored in bags in refrigerated warehouses.
These are storage systems in which the bags are not stacked in solidly constructed buildings. The main systems of open-air storage are:
The advantage of these systems is that they can be set up quickly and fairly easily. For this reason they are generally used when storage needs are specific and urgent.
Storage in pyramids
This system is often used for short-term storage in dry areas. It consists of stacking bags pyramids on platforms that can be protected in case of bad weather.
The platforms on which the bags are stacked must effectively protect the grain against termite attacks.
Covered by concrete or tar or made up of a layer of building-blocks covered with tarpaulins or plastic, the platforms must prevent the grain from exposure to rising damp.
To achieve this end, not only must the sites of the storage areas be carefully chosen but drainage ditch for rain-water runoff must be dug around the platforms.
To keep rain-water from falling on the grain, it is important to cover the pyramids of bags with tarpaulins.
This technique is frequently used for groundnut storage.
Storage in flexible silos
Storage in flexible silos is often used for setting up a security reserve and is very similar to storage in pyramids.
The main difference is the greater complexity of the storage facility.
A flexible silo is made of a concrete platform, generally circular in shape. Walls of galvanized screening about 2.5 metres high are erected around it and the inner walls lined with a thick film of plastic. On the outside, about 50 cm from the walls, galvanized metal sheets about 1 m high surround the silo to protect the grain from rodent attacks.
The bags stacked in the silo are covered with a conical tarpaulin attached to the walls and kept in place by a system of ropes.
Because these buildings are almost completely sealed, it is important to store the grain when it is very dry.
Flexible silos of 500 tonnes are the most common, but some are also built with storage capacities of 250 to 1 000 tonnes. The costs of building these silos are fairly modest, but their useful life is relatively short, seldom exceeding five years.
Warehouses and storehouses
Whether simple huts that farmers have turned into storehouses or modern well-equipped warehouses, storage buildings must meet the following requirements:
Location and orientation of the buildings
Effective protection of stored grain against atmospheric factors (sun, rain, humidity) and smooth operation of storage systems depend on good location and alignment of the buildings.
In this respect, the buildings to be used for storage must be:
Dimensions of the buildings
Storehouses are generally rectangular, about twice as long as they are wide. Appropriate dimensions of these buildings can be determined with a knowledge of:
The specific volume means, for each type of grain, the space occupied by a tonne of product stored in bags. Its unit of measurement is the cubic metre per tonne of product (m³/t).
The following table gives the specific volumes of some products stored in bags:
|GRAIN STORED IN BAGS||SPECIFIC VOLUME|
|Milled rice, wheat, coffee||1.6 m³/t|
|Maize, sorghum, groundnuts||1 8 m³/t|
|Beans, peas, lentils||1.3 m³/t|
|Sunflower seeds||2.8 m³/t|
|Soybeans, cocoa||2.0 m³/t|
|Wheat flour, maize flour||2.1 m³/t|
By multiplying the specific volume (in m³/t) by the quantity of grain (in t) to be stored, one obtains the volume (in m³) occupied by the bags in the storehouse.
Height of the stacks
The maximum height of the stacks depends on the type of bags used to store grain.
For bags made of plant fibre (jute, sisal, etc.) maximum heights can be 5-6 metres, while for plastic bags (woven polythene) they should not exceed 3 metres.
Furthermore, enough space must be left between the roof of the building and the tops of the stacks for a workman to move about freely.
Passages and corridors
The width of the passages between the batches can vary from 2 to 4 metres, while the corridors between the walls and the batches must have a minimum width of 1 metre.
The size and layout of service areas depend on the size of the storage system.
In addition to the actual storage places, provision should always be made for:
Diagram of storehouse: M Storehouse; P Stacks of bags; A Work area; B Office; R Shed.
The floor of the storehouse must prevent rising damp. To achieve this, a waterproof layer (asphalt, tarred cloth, plastic film) can be put under the cement flooring.
Walls are generally made of bricks or breeze-block, but may be of corrugated metal. They should be rough-plastered inside and out, and covered with light-coloured paint.
The roof must have an overhang of one-quarter to one-third the height of the walls, to prevent rain-water from blowing through the vents.
The vents must be of suitable dimensions, and cut into the tops of the walls, under the overhang on the long sides of the building.
They ensure aeration and ventilation of the storage areas and partial lighting of the storehouse.
In order to keep out birds, rodents and insects, these openings should be fitted with screens and mosquito nets.
The doorways must be wide enough for easy passage of people, maintenance equipment and products.
Preferably double doors made of metal, they should open outward and be protected by a porch-roof from the rain.
In order to guarantee good storage conditions and longevity, the buildings must be permanently monitored and any necessary upkeep done promptly.
Minor routine upkeep may consist of:
Good sanitation also means that the premises and surroundings must be carefully systematically cleared.
For good storage management, it is important to provide the storehouses with suitable equipment.
Some equipment is essential for good storage; some is less necessary but makes the work of the staff easier and less tiresome.
Depending on the size of storage systems, the following equipment is recommended for storehouses:
Equipment for handling
Bags of grain are generally handled manually and hand-carried.
To make this task easier, two-wheeled trolleys are used for unit transport of bags.
Remember not to use hooks, since they do considerable damage to the bags.
In big warehouses, bags are stacked with the help of a bag-conveyor belt, but in small storehouses the mobile bag-lift is preferred, being easier to use since it takes up very little floorspace.
The latter lifts bags one by one, however, while the former has the advantage of working continuously.
Equipment for reconditioning products
It may be necessary to recondition products whose quality seems doubtful on arrival.
In this case, a grain-reconditioning unit is needed. This is composed of two feed augers with hopper, a cleaner-separator, a device for insecticide treatment, a weigher-bagger, and a bag-stitcher.
Diagram of a reconditioning unit: 1 Hopper; 2 Cleaning; 3 Insecticide treatment; 4 Bagging.
Bags and pallets
Grain is packed in bags, of which the storehouse should have a good supply: bags made of plant fibres (jute, cotton, etc.) or plastic (polythene).
The choice of type of bag is important, as it determines the height of the stacks.
The bags are stacked on wooden platforms called pallets, in order to prevent direct contact of the bags with the floor. Pallets are indispensable for keeping the bags from the dampness that rises through the floor of the storehouse.
The selection or construction of lightweight pallets is recommended so that they can be more easily moved about within the storehouses.
For well-managed reception and storage of grain delivered or stored in bags, the following general rules must be observed:
Stacking the bags
Each type of product should have a space reserved in the storehouse.
To that end, lines can be painted on the floor, leaving open the inspection corridors between the walls and the stacks of bags, as well as the handling passageways facing the doors.
Before stocking, the condition of the pallets must be checked (make sure, for example, that no nails are sticking out).
To ensure stability of the stack, each bag should be stacked so that it is always covered by two other bags.
In addition, the walls of the stacks should slope toward the interior of the heap, and the more slippery the bags (especially plastic bags) the more pronounced their slope should be.
The bags can also be stacked in pyramids.
The height of the stacks is conditioned by the type of bags (bags made of plant fibre or plastic), by the fragility of the products to be stored and, obviously, by the very dimensions of the storehouse. Furthermore, the height of the stacks should not be greater than their width.
The use of bags of the same type and dimensions, and equalized stacks permit quick checks of the quantities stored.
In fact, by multiplying the number of bags in a layer by the number of layers in the stack, the total number of bags in each batch can be determined.
Once the stack has been erected, its contents must be checked and documented. To this end, forms must be filled out and kept up-to-date, reporting at least the following data: number of bags, date and details of reception, stacking date, date and type of insecticide treatments.
These forms must be filled out in duplicate: one copy for the storehouse administration; the other to be attached to a bag in the corresponding stack.
Storehouses must be frequently inspected to check the condition of the products and the buildings.
In addition to daily visits, more thorough inspections must be made every week or two, to prevent losses from rodents, insects and moulds. These inspections, which should preferably be made at the end of the day, should cover:
Finally, a thorough, overall monthly inspection of the installations and products is recommended.
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