Technology
Our Electrostatic Separation Technology
A proven process for water, chemical-free particle separation
Operating Principle
The STET electrostatic separator utilizes electrical charge differences between materials, produced by surface contact known as triboelectric charging. When two materials are in contact, the material with the highest affinity for electrons becomes negatively charged, while the other becomes positively charged. Electron affinity depends on the surface properties and will result in substantial differential charging of materials in a mixture of discrete particles.
How the STET Process Works
The entirely dry process, which requires no additional materials and produces zero wastes, works as follows:
- Material is fed into a thin gap between two parallel planar electrodes.
- The materials acquire opposite charges through interparticle contact.
- Charged particles are attracted to the electrode plate of opposite charge.
- A high-speed open-mesh belt moves differently charged particles toward opposite ends of the separator.
The continuous-loop high-speed belt creates counter-current flow of the separating particles, and triboelectric separation charging and recharging within the separator. This feature is unique to the STET separator.
Benefits of the STET Separator
The STET separator offers benefits to a wide range of industries and applications, including:
- It is entirely dry, requiring no water, chemicals, or wastewater treatment.
- It operates continuously.
- It consumes only a small amount of electrical energy —1-4 kWhr per ton of feed processed, depending on the density of the material processed — which is used to operate the belt motors.
- It is easily permitted, as the only emissions control device required is a dust collector for nuisance dust.
- Often, there is little or no pre-processing required for feed material to the separator other than size reduction to the appropriate particle size.
- Unlike other electrostatic processing equipment, it does not require high-temperature thermal pre-treatment.
- The separator design is relatively simple and compact. A machine designed to process up to 40 tons per hour (density-dependent) is approximately 30 ft (9 m) long, 5 ft (1.5 m) wide, and 9 ft (2.8 m) tall.
- The belt and associated rollers are the only moving parts, making maintenance both simple and infrequent.
- It is easy to operate, with rapid start-up and shut-down; rapid response to feed variability; automation of many functions; and requiring limited operator qualification.
- The electrodes are stationary and are composed of a highly durable material.
More Details on the STET Equipment Technology
The STET separator is a parallel-plate electrostatic separator, with the electrode plates oriented horizontally rather than vertically, as is the case in most parallel-plate separators. Additionally, the STET separator performs particle tribo-charging and conveying simultaneously via a high-speed open mesh conveyor belt. This feature allows for both a very high-speed processing rate as well as the ability to process powders much finer than conventional electrostatic devices.
Our separator machinery has been in commercial operation since 1995, separating unburned carbon from fly ash minerals (typical D50 approximately 20 µm) produced in coal-fired power plants. Our electrostatic separation machine has also succeeded in beneficiating other inorganic materials, including minerals such as calcium carbonate, talc, barite, and others. The STET separator has also been successfully applied to processing agricultural materials such as oilseed meals and pulses, animal meals, and rendering products.
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).
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 they 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.
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 of particles within the separator, eliminating the need for a pre-charging system upstream of the STET separator.
The proprietary 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 — affect the maximum feed rate typically to a lesser extent.
For relatively high-density materials such as 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.
Simple Operation
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 offers multiple automation options:
- On-board PLC Controls
- Auto-electrode gap adjustment
- Auto-belt tensioning
- Auto-belt tracking
- HMI (Human Machine Interface) touch screen controls
- Built-in alarm and fault functions that are dynamically generated for safe operation
- One-button auto-start/auto-stop features
FAQs
How does electrostatic separation work, and what materials can it process effectively?
Electrostatic separation works by electrically charging dry particles and separating them according to differences in their surface properties. It is particularly effective for fine particles that can be difficult to separate with conventional methods. The technology can process materials such as minerals, fly ash, calcium carbonate, talc, barite, and various food and feed ingredients.
What throughput or capacity can I expect from an industrial-scale electrostatic separator?
Industrial electrostatic separator capacity depends on the material, particle characteristics, feed preparation, and desired product quality. High-capacity dry separation systems can process up to 40 tons per hour, making them suitable for continuous commercial operations. Pilot testing is typically recommended to establish realistic throughput, separation efficiency, and operating conditions for a specific material.
How can I process dry minerals efficiently without using water or chemicals?
Dry minerals can be processed efficiently using triboelectrostatic separation, which separates particles according to differences in their electrical properties rather than relying on water or chemical reagents. This approach is especially useful for fine mineral particles and can provide continuous processing while avoiding dewatering, wastewater treatment, chemical handling, and the additional drying steps associated with wet separation methods.
How can I reduce energy and water consumption in my mineral separation process?
Switching from water-intensive beneficiation methods to dry electrostatic separation can significantly reduce or eliminate process-water requirements. Because the process does not require chemical reagents or subsequent drying of wet material, it can also reduce energy use in suitable applications. The best results depend on mineral characteristics, so material testing should be completed before selecting a separation process.
Can STET train my team to operate and maintain the electrostatic separator?
Yes. Operator training can be provided as part of the implementation and ongoing technical support for an electrostatic separation system. Training can help teams understand equipment operation, process controls, routine maintenance, troubleshooting, and optimization. This enables plant personnel to operate the separator safely and consistently while maintaining the required throughput and product quality.
