The Edinburgh Cohesion Tester (ECT) was developed with the financial support of British Coal Utilisation Research Association and UK Department of Trade and Industry to enable rapid assessments of a coal's handling characteristics.  It was designed to measure the unconfined compression strength needed to collapse a column of coal after it has been consolidated under a known pressure. CoalTech has recently conducted an ACARP project to evaluate the ECT for its suitability to determine the handleability of Australian coals.

Based on the work conducted at Edinburgh University and this project an ECT test procedure has been developed that will enable the Australian coal industry to quickly assess the handleability of their coals. The speed of testing of the ECT permits a substantial increase in the available information on the sensitivity of coal handleability to different key coal quality parameters. This tester can be easily transported and used by other laboratories.  Repeatable tests can be achieved with only 15 minutes of operator training.

CSIRO supplied twenty coals tested in ACARP project C24060 together with the handleability test results determined in the CSIRO’s laboratory scale rail wagon rig. Five of the coals were similar products to those tested by Casella CRE Energy in ACARP project 11016 - “Improved measurement of handleability for quality control of Australian coals in PCI and carbonisation applications”.  The testing conducted by Casella CRE Energy included handleability tests in a Johanson Indicizer System and an older model of the ECT.

The unconfined strength was determined on nineteen of the twenty coals, these were tested unsized and at the as-received moisture content. As Coal 20 is a sized coal with very little material below 2mm, no cohesion would develop in this coal under any consolidation load, and consequently, it was not  tested in this project.

The ECT tests were also conducted on nineteen coals that were air dried and the plus 19mm material removed. These minus 19mm samples were wetted to various moisture contents to examined the influence of moisture and consolidation stress on cohesion. The influence of moisture and stress is characterised by the Stress- Moisture-Cohesion (SMC) function.  From this function the maximum unconfined strength of a coal sample can be determined, the critical moisture is the moisture at which this maximum occurs.

Tests were conducted to determine the influence of top size and fines content on handleability.

The similar ranking of handleability by the different tests support the use of ECT to measure handleability. This is reinforced by the findings of other authors that the unconfined strength is the best measure for handleability problems associated with arching in bins or rail wagons. The maximum unconfined strength and the critical moisture at which this occurs seem to be the most important handling  properties of a coal product and ECT allows these to be measured effectively.

The ECT is a superior test to the Durham Cone for investigating the causes of handleability problems as it gives a better discrimination between coals that may or may not have a handleability problem.

ECT tests can be conducted on minus 50mm product, though sampling of a 2.5 kg sample required for testing will lead to greater variations when testing multiple samples of the same coal. This variation is due to sampling from the bulk sample as the test itself demonstrated good repeatability on one sample.  Edinburgh University has developed a much larger automated tester suitable for routine testing of full size range production samples.

For the coals tested, the coal properties identified as having a significant influence on the unconfined strength of the unsized as received samples were ash (%d), the slope of the Rosin Rammler distribution, and the CaO % in the coal.  Surprisingly moisture was not found to be a significant factor by the step-wise linear regression technique used in this project.

It was found that the ECT testing to determine SMC function can be conducted on a minus 19mm air dried sample and wetted as per this report.  It was shown that the maximum unconfined strength calculated from the SMC function correlates closely with the unconfined strength of an unsized as received sample when other coal properties are taken into account.

The results from ECT testing should allow a producer to predict what effect changes to ash or size distribution have on product handleability based on the SMC function determined for that product.

This research has demonstrated that ECT is an inexpensive, rapid, robust, easily used and repeatable tester for handleability assessment.