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Sutton Stoner Density Separators
A simple matter of equilibrium…that’s the secret of the Stoner. Using the principle of stratification in a fluidized product bed, the Stoner has the special property of retaining an inventory of heavy fraction to prevent loss of product with rejects. Named for its original application, the Stoner was developed over 50 years ago to meet the special needs of flour mills requiring the removal of stones, metal and glass, which could not be removed by screening, from wheat.
Sutton Stoner Separation Applications
Strictly a two-way separator, the Stoner removes a small amount of heavy material from large amounts of light, producing a clean, heavy concentrate without product loss. The Stoner differs from the Fluidized-Bed-Separator in that it cannot produce a clean product if particles of intermediate characteristics with respect to size, shape, or density are present. Whereas the Separator will classify these intermediates in a middling fraction, the Stoner does not have this capability.
Density Separator Function
The material is fed onto a flat, porous deck which vibrates with a straight-line reciprocating motion. Unlike the Separator, the Stoner deck slopes in one direction only. Heavy particles sink to the bottom of the stratified bed and are conveyed upward to the reservoir behind the discharge throat. The light product particles, lifted by the fluidizing air, flow down slope to the discharge spout at the lower end. The deck narrows toward the reject discharge throat to concentrate an inventory of heavy particles. This concentration, augmented by the resistance of the hinged gate show, causes the heavy particles to stay on the deck much longer than the light product particles.
The heavy reject pool, fluidized by both vibration and airflow, displaces the light product particles toward its lower boundary, thereby preventing loss of product with heavy rejects. By ejecting the heavy particles through the discharge throat at the same rate at which they enter with the feed, the Stoner maintains a constant inventory in the reject pool. Stoners work best in applications where the two components of the feed are sharply different in density but a like in size and shape, and where the heavy material is a relatively small percentage of the feed.
The original flour mill application meets these conditions because the wheat is closely sized in cleaning operations upstream from the Stoner. Inefficient screening, however, impairs Stoner performance. The fine sand or stone particles, if not eliminated through the sand screen, will not be rejected with heavy fraction, but will go on to the mill with the grain. Recovery of these finer particles of heavy reject material could be better with a Fluidized-Bed-Separator, which would return them with a middling fraction for re-screening.
Sutton Stoner Applications
So, why use a Stoner? For two reasons:
- Its capacity is greater per square foot of deck area.
- It has the ability to accumulate a pool of heavy rejects.
In the wheat cleaning application, the Separator, which lacks the ability to build a reject pool, cannot produce a clean reject due to the very small percentage of contamination in the incoming grain (between .002 and .005%). If the Separator were used in such an application, or in quality grading to remove undesirable light and heavy fractions, it would only concentrate the rejects. A small Stoner would be needed to recover the product mixed with the reject concentrate from the Separator.
A major invention in dry separation equipment, the Stoner, or specialized versions of it, has solved such diverse separation problems as the removal of:
- Stones, metal and glass from oilseeds prior to crushing or cracking to prevent roll damage
- Heavy foreign material from grain, legumes, and peanuts destined for human consumption
- Peanut kernel fragments from waste hulls, after shelling, for oilstock recovery
- Stones from wood chips to prevent refiner plate damage, replacing wet washers
- Tramp copper from aluminum granules in mechanical scrap wire reclamation systems
- Glass from composted solid waste
- Non-ferrous metallic prills from foundry sands
- Coarse particles (shives) from wood flakes for particle board
- Nodular iron pyrites from ground clay for brick and tile
Sutton Stoners Applications
Dry Material Separation Equipment FAQ
How is fluidizing air and controlled vibration used to separate a dry mixture? Using tuned airflow to stratify the material?
The lighter materials are lifted from the deck surface and allowed to float down the inclination of the deck. Heavier particles are in closer contact with an inclined vibrating surface. This vibration actually moved particles on the surface up the incline, opposite the lighter material not in contact with the vibration.
What is the most efficient way to accomplish separation?
First, you will want to screen the particles into manageable size ranges prior to separation. Where significant variations in shape are found to be detrimental to separation efficiency, size reduction or other process steps to change the shape may be added to reduce the range of variation. Moisture reduction may also be key to effective separation. Some materials absorb moisture and weight, others are complicated by the ‘sticky factor.’
What is the difference between the different models?
In general, there are two different model classifications, rectangular two-way separations and triangular offering a gradient of density out. The rectangular shape is commonly called a stoner. The triangular shape is commonly referred to as a gravity separator or air table.
When should I use a gravity separator?
The triangular shape, or trapezoidal, produces a fan or range of density output allowing one or more intermediate density fractions or “middlings.” In some processes, the middling fraction allows further separation efficiency by allowing other processes. This can be recycled intro further density separation.
When should I use a stoner?
It is used when separation of a smaller amount of dense material from a lighter product. The name is derived from separations of contaminants from agricultural products, but density separations cross into mineral, chemical and many other areas. A stoner may have a higher capacity and lower operator attention requirements, but offer less flexibility and precision.
