Adsorption Tracer Technology

The primary objective of this project was to develop an instrumentally based tracer detection system which would result in a cost effective on-line method for the measurement of separator efficiency in coal cleaning circuits.

The method would be based on the adsorption of low cost non-intrusive reagents onto the surface of coal particles which could subsequently be detected by instrumental methods. By the development of such a technique, the cost of plant audits would be lowered due to reduced manpower requirements arising from the lack of necessity for tracer recovery.

Objectives

Other objectives of the project included:

• Development and identification of a suite of adsorption-based tracers for use with raw mixtures which would enable passive instrumental interrogation of the products of separation processes.
• Illustration of the practicality of the method by in-plant demonstration on a selected separator.
• Identification of a lower cost alternative to the use of expensive polymeric tracers.

Results

A set of experiments was carried out to perform a preliminary assessment in a coal washery environment. This included testing the durability of proposed particle coatings, the suitability of machine vision with available lighting sources, and the required degree of instrumental robustness.

To this end, the feasibility of using coloured coal particles as cost-effective density tracers for determining the performance of coarse coal cleaning circuits was established. Coloured coal particles have the advantage of being sufficiently low cost to be considered non-retrievable and are totally geometrically compatible with existing washery feed.

The feasibility of using coloured coal particles as cost-effective density tracers for determining the performance of coarse coal cleaning circuits was established.

Washery trials involving visual detection confirmed that coloured coal tracers provided partition curves in close agreement with those derived from washability data based on conventional float-sink analysis. A prototype unit for the detection of coloured tracers by machine vision techniques was constructed and its efficiency demonstrated under both laboratory and washery conditions.

Only a small amount of additional research and subsequent development (at an estimated cost of $125,000) would be required to assemble a full on-line system from units similar to the prototype. Once the statistics for the detection of released tracers were established for any given circuit, determination of the efficiency of that circuit should be a low-cost procedure with machine vision monitoring.

The application of a coupled-pair array of three terminal magnetic sensors for the detection of magnetically-tagged coal particles in a coarse coal circuit was also demonstrated at the proof-of-concept stage.

However, the advantage of bulk sensing, rather than line-of-sight detection, is offset by the disadvantage of only a small number of different signatures provided by coal particles coated with low-cost and end-use compatible magnetic materials. In principle, coal particles bearing encapsulated microchip transponders would provide a solution to this problem for coarse coal, but the chips are currently too expensive for use with non-recovered tracers.

This situation is expected to change after smart cards have been widely accepted as a substitute for cash in the community at large, and after microchip supply has exceeded demand.

On the basis of the experiments involving coarse coal, the application of magnetic sensing to the detection of tracers in small and fine coal circuits appears to be feasible.

The demonstration of this latter approach was an integral part of the original two-year proposal which unfortunately had to be curtailed due to the unavailability of funding. On the basis of the results reported herein, this approach remains worthy of further study.

Conclusions

The feasibility of using coloured coal particles as cost-effective density tracers for determining the performance of coarse coal cleaning circuits has been established.

Washery trials involving visual detection confirmed that coloured coal tracers provided partition curves in close agreement with those derived from washability data based on conventional float-sink analysis.

A prototype unit for the detection of coloured tracers by machine vision techniques has been constructed and its efficiency demonstrated under both laboratory and washery conditions.

Only a small amount of research, followed by relatively straightforward development, would be required to assemble a full on-line system from units similar to the prototype. The cost of this option has been estimated to be $125,000.

The application of a coupled-pair array of three-terminal magnetic sensors for the detection of magnetically-tagged coal particles was also demonstrated at the proof-of-concept stage. However, the advantage of bulk sensing, rather than line-of-sight detection, is offset by the disadvantage of only a small number of different signatures provided by coal particles coated with low-cost and end-use compatible magnetic materials.

In principle, coal particles bearing encapsulated microchip transponders would provide a solution to this problem, but the chips are currently too expensive for use with non-recovered tracers.

This situation is expected to change after smart cards have been widely accepted as a substitute for cash in the community at large, and after microchip supply has exceeded demand.

On the basis of the experiments involving coarse coal, the application of magnetic sensing to the detection of tracers in small fine coal circuits appears to be feasible and should be pursued.