Coal Preparation » Gravity Separation
This handbook is intended as neither an introductory text, nor as a manual for detailed design. Rather it seeks to provide guidance for experienced circuit operators who are already familiar with coal-washing dense medium cyclones and their ancillary devices, circuitry and control systems.
Readers who require more general coverage and specific advice for Australian conditions are encouraged to consult other publications including Sanders (1) and Davis (2).
Dense medium cyclones were introduced into Australian washeries in the 1950s. Modern circuits continue to be based on the strong foundations provided by the Dutch State Mines and Stamicarbon BV, but over the ensuing decades, many innovations have been trialed. Many have been rejected and others have proven useful and have been widely adopted:
· Multislope screens provide higher drainage rate and smaller footprint by comparison with original sievebend and low head combinations;
· Cyclones of larger diameter and cyclones with larger-than-conventional orifices provide higher capacity per unit and allow processing of larger particles;
· The adoption of gravel pumps, including large capacity 20/18 units, facilitates the feeding of large DMCs with large feed topsize;
· Hard-wearing DMC lining materials, especially high alumina tiles, allow high tonnages to be processed between maintenance shutdowns for DMC replacement or refurbishment;
· Some DMC designs replace tangential inlets with slowly-tapering so-called evolute entries which may also be scrolled. These reduce wear and increase capacity and may improve partitioning efficiency;
· Variable speed pump motors allow more stable control of flow rate, pressure, medium to coal ratio and cutpoint;
· Static or flume screens are used before multislope drain and rinse screens;
· New generation magnetic separators achieve adequate magnetite recovery in a single stage, eliminating the need for a secondary circuit.
By synthesizing the highly valued, prescriptive DSM recommendations with subsequent research and with experience of the newer generations of equipment and circuitry, this publication seeks to provide operators and process engineers with a tool to explain dense medium cyclones and to assist them in optimizing performance of DMC plants of both modern and venerable design.