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Safe Storage & Handling of Grains

14 May 202014 min reading

It is important for the individuals responsible for growing, buying, storage, handling and processing grain to know the handling systems. Storage facilities, handling systems, and atmospheric conditions can significantly affect the quality and value of the grain. Grain grading systems reflect damage to grain that occurs during storage and handling. Unsuitable mechanical equipment can cause changes in quality such as increase in kernel breakage and amount of fine dust in the grain. The penetrating and residual musty odor coming from mold growth is a concern in grain grading; accordingly, such grain is designated as smutty. Heat damage results from conditions developed during storage.

Karan Singhal Senior Cereal Miller and Consultant

While sprawling world commodity prices have taken their toll on the grain handling industry, there is still strong demand for new projects and expansions in several regions throughout the world, which is further adding competitive pressure on the industry. In such situations safe storage & proper handling of grain technique comes as a savior. How can we balance the needs of a growing world population against the limits to growth that may be imposed by the diverse environmental consideration globally? Whatever the pressures, whatever the solutions, one thing is certain: Grains will continue to be center stage in world efforts to feed a growing population. With safe storage, proper grain handling, we can escape the confines of the nation in the Byzantine proverb.

It is important for the individuals responsible for growing, buying, storage, handling and processing grain to know the handling systems. Storage facilities, handling systems, and atmospheric conditions can significantly affect the quality and value of the grain. Grain grading systems reflect damage to grain that occurs during storage and handling. Unsuitable mechanical equipment can cause changes in quality such as increase in kernel breakage and amount of fine dust in the grain. The penetrating and residual musty odor coming from mold growth is a concern in grain grading; accordingly, such grain is designated as smutty. Heat damage results from conditions developed during storage.

According to the U.S. grading system, more than 0.2% heat-damaged kernels degrades grain to No. 3 grade. Such physical, chemical, and biological changes in grain quality can be avoided if conditions during storage and handling are properly controlled.

INTRODUCTION The infrastructure associated with grain storage is a major component of the grain management system. A grain storage and handling facility includes grain receival, grain movement, grain cleaning, reclaim, cleaning and storage operations. This is a major investment and the whole system must be carefully planned. Facilities for the storage and handling of grains (and processed grains) should be compatible for whole grains, ground grains or processed grains.

Design Objectives Grain storage and handling facilities should be designed, constructed and maintained to ensure that

• Process flow and layout of the distribution system is suitable for the types and characteristics of the materials to be handled and the operational requirements of the facility. • Quality of the grain handled is not compromised by contamination by insects or rodents. • Personnel, equipment and overall facility safety issues are implemented.

Mandatory Requirements Compliance with • AS1657 -1992 Fixed platforms, walkways, stairways and ladders – Design, construction and installation for access, stairs, landings etc. on grain storage and handling equipment. • AS2865-2009 Confined Spaces for confined spaces entry requirements.

Facility Layout The type of construction and the amount of available land may determine the physical layout of the facility. The relative location of the areas designated for grain receival, feed preparation, loading and feeding out will affect the operational efficiency and costs of running the facility. Design considerations for each storage and handling facility should include • Storage capacity • Handling rates • Capital cost • Short-term (e.g. pad/bunker) versus long-term (e.g. silos) infrastructure • Allowable level of grain degradation • Protection of grain from spoiling, insects, pests and vermin • Maintenance requirements • Process flow/layout requirements • Automation • Lot identity conservancy • Built in flexibility • Expected life of the system • Safety (e.g. dust explosions).

Grain Characteristics Grains can be divided into three groups: cereals (maize, wheat, barley, sorghum, rice); pulses (lupins, beans, peas); and oilseeds (soybeans, sunflower, linseed, canola).

Different grains and grain types have a range of characteristics that can affect the type of distribution system selected and the components required in the distribution system. These characteristics include moisture content, respiration of the grains, angle of repose of the grains, abrasion of the grains against contact surfaces and ease of flow of the grains. A brief description of moisture content and angle of repose follows.

Moisture Content Moisture content in grain is defined as the amount of water that is absorbed into the grain kernel as a percentage of the total weight of the grain kernel. The moisture content of a grain is typically provided on a ‘wet basis’ (wb) and is calculated as

Standard grain grades with moisture contents of 13–18% do not usually cause material flow problems. But high moisture content grain, when coupled with high foreign material contents and fines, can lead to material flow and handling problems. Moisture content of the grain can change with the environment in which it is stored and this should be monitored to help ensure the overall condition of the grain.

Graphical representation below illustrates the potential issues with stored grain at a range of temperatures and moisture contents. As the temperature rises, the safe level of moisture in the grain must be reduced for good quality storage.

Moisture and Temperature changes in stored grains air movement inside the storage The migration of moisture in stored grain takes place due to change in temperature as per season i.e. winter and summer. One of the most important factors influencing storage life of the grain is moisture content. High moisture content and a warm climate promote mold growth, insect growth and increase rate of respiration of grains and due to this deterioration and losses of the stored grains takes place. Moisture migration takes place in stored bin even though the grains are stored at a desired moisture level i.e. safe for storage.

Angle of Repose The angle of repose is the greatest angle from the horizontal to which a grain can be raised without it sliding or rolling on itself in an unconsolidated form. This determines whether a grain mass will flow by gravity, or need outside forces to move. It will determines the minimum spouting angles for gravity flow. The angle of repose of grains varies with type, variety, moisture content, quality and level of contamination. Angle of Repose for common grains is shown below. These angles will increase for wet grain and may also vary slightly

Abrasion All grains will wear the surfaces that are in contact with flow. The amount of wear will vary according to the type of grain, the volume of grain, speed of grain, the impact of grain streams on surfaces and the slope of the contact surface. All aspects of the distribution system are affected by these characteristics. When analyzing systems, components such as spouting, transitions, gates, valves, conveyors and future access to these components must be designed into the system for maintenance requirements.

Corrosion Wet grains, ground processed grains and chemically treated grains can corrode standard carbon steel fabrications. Each grain type to be handled must be checked to determine if stainless steel is needed, or will reduce possible life cycle costs. If water wash down, or cleaning place systems are required, materials used for fabrication in the distribution system should be considered.

Respiration of Grains Grains get oxygen from the air and burn food from its endosperm. This process liberates heat, water vapors and carbon dioxide. This process in grains is called respiration. The respiration in grains, during the storage period, causes a dry matter loss of 1% or more.

Respiration is a process of slow combustion of carbohydrates in presence of oxygen in living system to produce the energy.

C6H12O6 + 6O2 —> 6CO2 + 6H2O + Energy

This process is affected by temperature and concentration of O2 and CO2. Decreasing the concentration of O2 and increasing concentration of CO2 reduces the rate of respiration. A decrease in temperature slows down the respiration rates in grains like many other foods.

Grain Storage All storage systems must be designed to adequately protect and preserve the quality of the grain. Whole grain can sprout under certain conditions and will also attract moulds, insects and rodents. In addition, the storage of grain presents several safety issues. Grain storage systems come in a range of shapes and sizes, design of a grain storage facility should be based on • Length of time for storage – temporary or long-term. • Degree of segregation of different types of grain. • Identity preservation requirements. • Expected useful life of the structure.

Long Term Storage In general, grain in long term storage should be held cool and dry. Options include smooth wall steel silos, corrugated steel silos bins, concrete silos and underground pits. Steel silos are the most common method of long term storage for grain at feedlots, but underground pit storage is an alternative for longer term storage.

Silos Silos are available in a variety of sizes, configurations and materials, including flat bottom or cone base, gas-tight sealable or non-sealed, aerated and non-aerated. Silos can be built on site or transported fully constructed and ready to stand. The size of fully constructed, transportable silos is limited by road transport regulations. As a general guide, fully constructed silos can be up to 140t capacity. Most small (50–70t) cone-bottom silos are generally prefabricated and transported. Cone-bottom silos are self-emptying, but are limited to capacities of less than 300t. Feedlots may require air-tight/gas-tight storage facilities of higher capacity. But the increased surface area of a larger silo requires more sheet metal joins, providing more opportunity for air or gas to escape. Capacity is commonly quoted in tones, but may also be quoted as cubic meters (m3). To determine tonnage capacity, multiply the cubic capacity by the bulk density of the grain.

Silo Foundations Foundations for elevated silos are different to those for general building construction because of the large loads involved. The first step in establishing a silo is to construct a good quality pad. These structures are engineered to support grain in a vertical plane, with pressure exerted and distributed evenly around the base support frame. If the pad is not level, the weight of the grain will place excessive stresses on the lower sheets of the silo and possibly twist the base frame - deforming the silo. The soil engineering requirements for most elevated silos should be determined by a consulting geotechnical engineer.

Silo Safety Safety issues associated with grain storage and handling include working at heights, working in confined spaces, entering grain silos while being emptied (grain entrapment) and dust explosions. Silo designs now incorporate ground operated lids, caged ladders, platforms and top rails to minimize the risk of operators falling. Facilities for harness attachments, which should be worn by all operators who are climbing and entering silos, should also be fitted. Silos are classified as confined spaces and correct procedures need to be followed prior to entry.

Grain Storage Management Good hygiene in grain handling and storage premises will maintain the quality of the products handled. Problems with grain caking on silo walls, being damp and mouldy in the base of the store and sprouting in the headspace are caused by poor grain management or poor maintenance of the grain store. Other problems have been reported with lupins or peas stored in old silos, where walls have buckled or compressed from the greater pressure exerted by the round seeds. In extreme cases, the silo has collapsed. Good hygiene can be achieved by ensuring that storages facilitate are • Easily inspected. • Regularly serviced for equipment maintenance. • Cleaned of grain residues, particularly in sheds, around silos, in augers and in silos after emptying. Good storage design should be complemented by • Correct training of people in safety and hygiene-related issues. • Regular monitoring. • Establishing a system for recording and checking hygiene procedures.

• Developing action strategies if contamination is to occur.

Grain Handling Grain handling and conveyor systems should be designed to minimize damage to grain. Pulses are more susceptible to impact damage than cereals and should not be moved in pneumatic grain conveyors, as the impact speed of grain is higher than the critical 12m/s. Augers smaller than 125mm in diameter should also be avoided with pulses. Augers should be run full, and preferably slow, to reduce grain damage.

Grain Receival Hoppers A high capacity receival system is needed for efficient transfer of grain. Ideally, it should be possible to deposit a trailer load and pull away from the unloading area within minutes. An in ground receival hopper is typically fitted with a screw conveyor, or auger, to raise grain for conditioning or storage.

Grain Conditioning and Metal Detection Foreign materials and dust must be removed to eliminate problems further down the grain storage and handling system. A grain conditioner, or scalper, removes foreign particles. A dust extraction and collection system prevents dust entering the environment. All foreign metal objects must be detected and removed before they can cause damage. A permanent or electro-magnet must be located in the chute that feeds the grain conditioner, but needs to be checked and cleaned regularly.

Belt and Bucket Elevators Bucket elevators are used mainly to lift grain vertically to silos. These usually deliver the grain directly into silos using diverters that direct grain into a gravity chute to the selected silo, or by using belted conveyors to transfer grain horizontally to the various silos. The capacity depends on the volume of the buckets, the spacing and the speed of the belt. Elevators up to 20m high and with a capacity of 50t per hour are available. Bucket elevators are self-cleaning by design and are typically fixed in position.

Auger (Screw Conveyors) Auger elevators are one of the cheapest methods of elevating grain and can be fixed or portable. These are available in a wide range of lengths and capacities. They are comparatively light in weight, dependable in operation due to good portability. Long augers may be mounted on wheels for easy transport. The angle of operation is adjustable, but the capacity declines as the auger is raised. High moisture content in grain also reduces the capacity of the auger. Old augers with worn flighting can damage split-prone grain.

Belt Conveyors Belt conveyors are typically used to transfer grain horizontally. Inclines up to 15° are possible - and even up to 30° with ribs fitted to the belt. Belt conveyor capacity is high and grain can be loaded or unloaded anywhere along the belt. Belt conveyors do not damage the grain and raise little dust.

Drag Chain Conveyor Drag chain conveyors, or paddle conveyors, use a series of paddles fixed to a loop of chain moving inside a fully enclosed conduit. The circular paddles are sized to fit snuggly in the conduit. This fully enclosed system prevents dust in a building. Drag chains can move grain at any angle, including horizontal, and are largely self-cleaning, although corners of the chain loop will typically require attention. Drag chain conveyors are a permanent installation, but can be easily extended for facility expansion.

Mobile Equipment Mobile augers, mobile belt conveyors, grain throwers and pneumatic conveyors may be used to load grain into storage facilities. Mobile augers or belt conveyors, with fixed and guarded cross sweeps, or a front-end loader can be used to empty the pad. Pneumatic conveyors also suit this job and allow easy final clean-up of grain. Operators using mobile elevating equipment must be made aware of any overhead power lines to prevent electrocution.

Automation Controls, instrumentation and automation systems are key elements in the overall distribution system. The automation system is governed by the overall facility design and operational requirements. Each individually controlled device can be linked into a main PLC, enabling coordination of the controls between various equipment.

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