Evaluation of the Edinburgh Cohesion Tester
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.