Most people first encounter silica sand during childhood, while playing in sand boxes or at playgrounds. Unlike beach sand, which is mainly derived from limestone, silica sand is made up of quartz crystals, which are found in abundance in earth's crust. The crystals are extracted by mining and then processed into the various grades of silica sand. Also known as quartz sand or industrial sand, silica sand is an important component for a variety of industrial and construction uses. The use of silica sand is determined by its structure and physical properties. For example, the chemical composition of the silica sand is highly relevant when the silica sand is used in glassmaking, while the grain hardness is an important facet when the sand is used for sandblasting.1

Among the major applications of silica sand are as an abrasive to grind and polish metal, part of the content of building products such as bricks and roofing tiles, in glassmaking, as a refractory agent and as a proppant in the hydraulic fracturing of gas and oil wells. It is also used in the manufacturing of paints, as a filtration material for water and other potable liquid systems and in golf courses, volleyball and other athletic fields.

The characteristics of silica sand that determine its use are cleanliness, (which refers to the ratio of silt, clay and organic matter in any measure of sand); color, (shades of brown or orange indicate the presence of impurities such as iron oxides); as well as grain size, shape, particle size range and refractoriness (melting point).

Characteristics and Challenges:

Due to the abrasive characteristics of the material, a silica sand conveying system must be rugged enough to withstand the impact of the sand on the interior
surfaces and moving parts of the convey line and equipment. With an average bulk density of 81 lbs/cu ft 2, silica sand is generally free flowing. Entry of sand particles into gears, valves or other fine motion equipment could result in damage and permanent reduction of performance quality. In some applications, the shape and purity of the silica sand is important, so care must be taken to avoid degradation while handling it. The very fine particles of sand can pose a health hazard, as breathing in the dust can cause silicosis, which in severe cases can be disabling or even fatal. Coarser particles of silica sand tend to interlock, potentially impeding their flow into downstream processing equipment.

Due to the degradable nature of silica sand, care must also be taken to maintain an air-line velocity during pneumatic conveying that does not damage it. The blower used to move the sand though the convey line must be sized to meet the system. Above all, preventing silica sand's abrasive properties from damaging the convey line should be a top priority. Equipment selection is paramount to ensure the longevity of the system.

If the silica sand arrives at the processing facility in bulk bags, the frames used to discharge the bags should ideally be equipped with additional accessories to completely empty the silica sand from the bag. This includes features such as spring-loaded frames that will elongate and stretch the bags, making them rigid and removing any pockets of silica sand cornered in the bags. Some of these bag activating devices also serve as a dust seal between the bulk bag and the receiving hopper.

After the bulk bag has been connected to the receiving hopper and the silica sand begins to flow, the air inside the hopper is forced out. Dust suppression during the dumping and de-gassing of the bulk bags can be achieved by use of a high

Silica Sand
volume fan drawing dust into cartridge filters. This arrangement can also act as a vacuum that completely evacuates the bulk bags post discharge, eliminating the potential dusting that could occur when the bags are removed and folded prior to storage or disposal. The cartridge filters can also be activated by an automatic reverse-pulse filter cleaner that returns the filtered silica sand dust into the receiving hopper, reducing material waste and lowering the risk of a potentially dangerous dusting.

If the sand is being fed into the processing system out of smaller bags, a bag-breaking station with a dust hood, filtration devices and a pneumatic pulse cleaner is the recommended solution to support the manual unloading of the material. A hopper screen above the receiving vessel will help to prevent the introduction of foreign objects and protects the operators from moving components inside the hopper.

If a flexible screw is being used to convey the silica sand, it is important to use a screw that matches the silica sand's characteristics and other application requirements. Generally a screw with a round profile will be effective in moving a material with silica sand's features. Due to silica sand's abrasive nature, a flexible screw with a heavy duty design is recommended.

Should your silica sand application feature the loading the material into bulk bags, the bag capacity will be maximized by use of a vibratory densification deck to
level the sand as it fills the bag and by the application of load cells to achieve the desired weight. Seals and other dust containment devices will ensure a dust-tight operation.

Flexicon Applications:

Consultation with a Flexicon specialist will help you decide if a flexible screw or pneumatic solution best fits your silica sand application. Flexicon's expert design and engineering staff will weigh each parameter and recommend the best solution for you. Upon request, Flexicon's test lab will simulate your silica sand handling applications before the system is installed in your plant.

Flexicon's Dust Suppression and Collection Systems ensure proper containment of silica sand throughout the conveyance process. Flexicon's BLOCK-BUSTER® Bulk Bag Conditioner loosens bulk solid materials that have solidified during storage and shipment, enabling bulk bag unloaders to discharge the material through bag spouts.

Flexicon's product line of advanced flow promotion conveyors, high flow hoppers, deaeration/densification decks and a host of other components and accessories are proven performers that promote flow while reducing degradation, dusting and/or the separation of blends comprised of disparate particles.

1 Research Council of Alberta
2 Powder Bulk Solids Bulk Density Chart
Sources: Where noted. All other information courtesy of Flexicon Corporation.


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