Spiral concentrators are used typically to clean the 1 mm X 0. 149 mm size fraction of coal. In recent years, improved performance has been obtained by using two stages of spirals configured in a rougher-cleaner with middlings recycle circuit. This circuit has been mimicked in a single spiral assembly by Multotec Process Equipment (Pty) Ltd of Spartan, South Africa, with the SX7 or seven-turn spiral. Successful applications of this spiral are found throughout the United States in Pennsylvania (both anthracite and bituminous), West Virginia, Kentucky, Virginia, and Illinois. These applications include cleaning a typical 1 mm × 0. 149 mm fraction of raw coal, treating the rejects from a water-only cyclone, and cleaning 1 mm × 0 anthracite followed by classification. Looking for additional options for ultrafine coal cleaning, Sedgman has applied this two-stage spiral to a finer size: the 0. 149 mm × 0. 044 mm fraction. This circuit has been applied successfully in two applications in the US, showing improvement in clean coal ash and, perhaps more importantly, pyritic sulfur. This paper will discuss the performance of the two-stage SX7 coal spiral for the applications mentioned, including the ultrafine applications used as a replacement for froth flotation. It will also discuss the desliming cyclone circuitry required for the ultrafine applications.
展开▼
