ACARP Project Number: C15070
Published: July 09
Philip Bennett, Johan Kosasi
Extended
Abstract
Based on the work conducted at Edinburgh
University and a previous ACARP project C15070 (Bennett, 2005), a
test procedure using the Edinburgh Cohesion Tester (ECT) has been
developed that enables the Australian coal industry to quickly
assess the handleability of their coals. The speed of testing of
the ECT provides a substantial increase in the available
information on the sensitivity of coal handleability to different
key coal quality parameters.
This project is a continuation of the previous
ACARP project. The objectives of this work were:
- To
determine the cohesion strength of the actual coal that has
difficulties during train wagon unloading. Therefore, identify the
upper limit of cohesion strength of coals that can be transported
in different rail wagons;
- To
investigate the influence of moisture, fines and clays on
handleability, thereby giving a rigorous basis for improved
understanding of the development of handling characteristics of
blends; and
- To
conduct trial blending experiments to investigate the effectiveness
of the ECT in predicting the handling characteristics of blends
when the cohesion strength characteristic of the component coals is
known.
These objectives have been achieved. The main
conclusions are:
- A coal
with cohesive strength of above 2.5 kPa may have wagon discharge
problems;
- The
maximum cohesive strength is due to interparticle capillary force
in the pendular regime. The interparticle force is related to the
properties of the coal, namely the water contact angle and the
filling angle;
- The
moisture content of the coal when this maximum cohesive strength
occurs is related to the water thickness on the coal particle which
depends on the properties of the coal;
- The
biggest difficulty in the prediction of cohesive strength is the
determination of the porosity at a given consolidation load. At
this stage there is no simple method that has proven to be
applicable to a wide rank of coals;
- Kaolin
and bentonite influence cohesion in two different manners. Kaolin
does not seem to alter the surface tension. Bentonite may change
the force required to separate bodies bonded by a clay suspension
due to viscous dissipation and not cohesion; and
- When
blending coals, the cohesion of the blend can be determined by
linear relationship between maximum cohesive strength and critical
moisture. This means that to predict the cohesion of a blend one
must have the stress moisture curve of each component coal.
