Spiral concentrators have been widely used in coal preparation plants worldwide to separate high-density materials from low-density materials commonly in the particle size range of1 mm x 150 micron. Recent studies also report the high efficiency separation obtained for fine coal cleaning up to a bottom size of45 micron. The major factors which have made spiral concentrators so popular include low capital and operating costs, requirements of no chemical reagent or dense medium, and the ease of operation and maintenance. However, not much work has been reported on automatic control of spiral performance with fluctuating feed characteristics commonly encountered in a real-life plant environment.

The main objective of this study was to develop a low cost microprocessor-based control system for automatic adjustment of the splitter position of a spiral concentrator to maintain desired density cut-points irrespective of fluctuations in the plant feed. The main research tasks included the development of sensing measurement system, setting up the microcontroller truth table, and integrating the entire system so as to actuate a servo motor to adjust the spiral splitter position based on real-time measurements. Several alternative sensing/measurement schemes were investigated, including ultrasonics, pressure mats and mechanical systems. It was determined that a mechanical strain gage based system is an inexpensive system having a potential near-term application for fine coal cleaning. A complete control system was developed using the mechanical sensor and a micro-compressor-based servo motor to adjust the splitter position of an operating spiral. While the feasibility of this automation concept has been proved using a lab-scale spiral, it needs significant modifications and refinements for its application in a full-scale spiral operating in a plant environment.