The micronized-magnetite coal cleaning technology is based on widely used conventional dense-medium cyclone applications, in that it utilizes a finely ground magnetite/water suspension as a separating medium for cleaning fine coal, by density, in a cyclone. However, the micronized-magnetite cleaning technology differs from conventional systems in several ways:
- It utilizes significantly finer magnetite (about 5 micron mean particle size), as compared to normal mean particle sizes of 10-20 microns.
- It can effectively beneficiate coal particles down to 30 microns in size, as compared to the most advanced, existing conventional systems that are limited to a particle bottom size of about 150 microns.
- Smaller diameter cyclones 10 to 25 cm (4 to 10 inch) are used to provide the higher G-force required to separate the finer feed coal.
- Cyclone feed pressures 3 to 10 times greater that those used in conventional cleaning systems are employed to enhance the separating forces.
- More advanced magnetite recovery systems, including rare-earth drums or high-gradient magnetic separators, are required for recovery and reuse of the medium.
Figure 1 contains the block flow diagram of the ET circuit that Custom Coals has installed in the PRF, and is presently testing. The circuit consists of three subcircuits:
- Classification Circuit – Which consists of a 5- cm (2″) Krebs Classifying Cyclone in combination with a Sizetec Inclined Desliming Screen. This circuit is equipped with various cyclone orifices and screen panel sizes to make a separation at 30-40 microns, removing the ultrafine particles to the waste via the cyclone overflow. The classification circuit receives feed slurry from the PRF at about 40 Wt% solids, and delivers a final product to the dense-medium cycloning circuit at about 50-60 Wt% solids, 225 Kg/hr (500lb/hr) of principally 300 by 30 microns particles.
- Dense-Medium Cycloning Circuit – Which consists of two parallel Krebs Dense-Medium Cyclones 5-cm/10-cm (2″ & 4″) diameter. The 10-cm (4″) cyclone products always recirculates back to feed, and is used for closed-loop testing. The 5-cm (2″) cyclone products progresses to the magnetite recovery circuit, and is used for the open-circuit testing. Magnetite is added on a controlled basis from the Magnetite Bin to maintain the desired correct media specific gravity.
- Magnetite Recovery Circuit – Which consists of a Sizetec Inclined Desliming Screen (Drain Screen), and a Sizetec Horizontal Dewatering Screen (Rinse Screen). The circuit also consists of four Eriez Conventional, Wet-Drum Magnetic Separators configured as primary, secondary, tertiary, and cleaner separators, and an Eriez High Gauss, Rare-Earth Magnetic Separator to be used as a final scavenger. The final magnetic concentrates report to the Correct Medium Sump and the scavenger tailings to the Waste Sump. The Waste Sump discharge is dewatered using the PRF’s existing Sharpies Horizontal Centriftige and Thickener, and all clarified water recirculates for reuse in the circuit.
In addition to the equipment shown in Figure 1, the ET circuit also contains a clarified water head tank and pump to provide all water additions to the circuit. A Motor Control Center (MCC) and Control Cabinet provide the power distribution and the required circuit control.
The magnetic content of the primary magnetic separator concentrate was at least 95% magnetics for all eight tests.