Characterise Cokes for Strength and Reactivity - Stage Two

To better understand how coal transforms into coke requires the ability to relate the main microstructural and microtextural features of the coke to properties of the coal. This project aims to identify the influence of these features on coke quality.

There are two parts to this project:

1. Optical imaging to determine the fused and unfused components of the coke structure. Subsequent analysis of the unfused component for shape, size and porous feature and the fused component for pore structure;

2. SEM based mineral analysis techniques to identify changes due to mineral phases would also lead to better understanding of the major mineral related factors influencing coke degradation after reaction with CO2.

Optical Imaging of Coke to Examine Coke Strength

In this extension the image analysis techniques developed in ACARP Project C18043 (Bennett, et al., 2012) were to be further developed to allow the determination of the size of the unfused material. As discussed in this report this approach was not taken and manual identification of the unfused components was carried out to ensure similar unfused structures were identified as Kubota et al. (2008). The criteria used in the identification of an unfused region was that it was a region that was mostly inert-derived maceral component (IDMC) and had the same structure within that region. A wide range of parameters were determine from the identified unfused regions and remaining fused structure which were related to coke strength, in particular coke drum indices.

MLA Characterisation of Minerals

In order to better understand the effect of mineral matter on coke reactivity, Mineral Liberation Analysis (MLA) was used to categorise the minerals on the surface of a prepared coke core. This core was then put through a reactivity rig before having the surface of the core imaged again using an optical microscope to observe the topology of the surface.

Recommendations

Imaging of coke to determine structural features is not a cost effective tool for the evaluation of coke and thus determining the value of the feed coking coal. The investment in this project by both ACARP and ALS Coal will only be realised if the coke structural features identified in this project can be linked to properties of coal. While it has been demonstrated that the fused and unfused parts of the coke structure are related to Vitrinite and Inertinite, it is the size of the Inertite (> 95% Inertinite) or Inertinite Dominant grains that is of most importance to the Australian coking coal industry. ACARP Project C24058 will examine how this may be done using CGA developed by CSIRO.

The image analysis techniques used to determine the strength of structures are continually evolving, mostly in the areas of metal foams, biological cell structure and bone structure. To assist further understanding of coke structure ALS Coal will make available all images and software to researchers in the field of coke structure.

The use of MLA and optical imaging of coal assist in clarify the role the minerals are playing. The combined understanding of the coke structure and association of minerals with the different regions within that structure will allow producers to be better understand what maybe influencing the coke quality produced from their coals.