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
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
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
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
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