The STET separator is a parallel plate electrostatic separator, however, the electrode plates are oriented horizontally as opposed to vertically as is the case in most parallel plate separators. Furthermore, the STET separator accomplishes the particle tribo-charging and conveying simultaneously by a high-speed open mesh conveyor belt. This feature allows for both a very high specific processing rate of feed, as well as the capability to process powders much finer than conventional electrostatic devices. The STET separator has been in commercial operation since 1995 separating unburned carbon from fly ash minerals (typical D50 approximately 20 µm) in coal fired power plants. This electrostatic separation device has also been successful at beneficiating other inorganic materials, including minerals such as calcium carbonate, talc, barite and others. The STET separator has also been successfully applied to processing gricultural materials such as oilseed meals and pulses, and animal meals and rendering products.
The fundamental details of the STET separator are illustrated below. The particles are charged by the triboelectric effect through particle-to-particle collisions within the gap between the electrodes. The applied voltage between the electrodes is between ±4 and ±10 kV relative to ground, giving a total voltage difference of 8 – 20 kV across a very narrow electrode gap of nominally 1.5 cm (0.6 inch). Feed particles are introduced to the STET separator at one of three locations (Feed Ports). The STET separator produces only two products, a negatively charged particle stream collected on the positively charged electrode, and a positively charged particle stream collected on the negatively charged electrode. The products are conveyed to the respective hoppers at each end of the STET separator by the separator belt, and fall out of the separator by gravity. The STET separator does not produce a middlings or recycle stream, although multiple pass configurations to improve product purity and/or recovery are possible.
Particles are conveyed through the electrode gap (separation zone) by a continuous loop, open mesh belt. The belt operates at high speed. The geometry of the belt serves to sweep fine particles off the surface of the electrodes, preventing the accumulation of fine particles that degrades the performance and voltage field of traditional free fall parallel plate type separation devices. In addition, the belt generates a high sheer, high turbulence zone between the two electrodes, promoting tribo-charging. The counter-current travel of the separator belt allows for continuous charging and re-charging or particles within the separator, eliminating the need for a pre-charging system upstream of the STET separator. The STET separator is a high feed rate, commercially proven processing system. The maximum processing capacity of the STET separator is mostly a function of the volumetric feed rate that can be conveyed through the electrode gap by the STET separator belt. Other variables, such as the speed of the belt, the distance between the electrodes and the aerated density of the powder effect the maximum feed rate, typically to a lesser extent. For relatively high density materials, for example fly ash, the maximum processing rate of a 42 inch (106 cm) electrode width commercial separation unit is roughly 40 – 45 Tons per hour of feed. For less dense feed materials, the maximum feed rate is lower.
|Feed Material||Approximate Compacted Bulk Density||Approximate STET 42 Inch Separator Maximum Feed Rate|
|Fly Ash||60 – 80 pound/ft 3 (1000 –1300 kg/m3)||40 – 45 Ton per hour|
|Talc||30 – 40 pounds/ft 3 (500 – 600 kg/m3)||15 – 20 Ton per hour|
|Wheat Flour||30 – 40 pounds/ft 3 (500 – 600 kg/m3)||15 – 20 Ton per hour|
The STET separator provides end users with adjustable control of product quality, and can be integrated into existing process flowsheets. In addition, the STET separator has multiple automation options:
STET currently offers two sizes of the STET separator:
This machine is approximately 9.1 meters (29 feet, 11 ¾ inches) long; 1.7 meters(5 feet, 7 inches) wide; 3.2 meters (8 feet 1 7/8 inches) high. The compactness of the system allows for flexibility in installation designs and processes up to 40 tonnes per hour for fly ash.
The power consumption is about 1 kilowatt-hour per tonne of material processed, with most of the power consumed by the two 50 HP (37 kW) motors that drive the belt.
This machine is approximately 9.1 meters (29 feet, 11 ¾ inches) long; 1.2 meters(4 feet 1 inch) wide; 3.2 meters (8 feet 1 7/8 inches) high, making it 18” narrower than or 42” model, and is able to process up to 23 feed tons per hour.
The power consumption is about 1 kilowatt-hour per tonne of material processed, with most of the power consumed by the two 30 HP (22KW) motors that drive the belt.