Fusibility of Coal Blends and Minerals in Coking

The CSIRO optical reflected light imaging CGA (Coal Grain Analysis) system was developed and enhanced with ACARP support to provide compositional information on individual coal grains for many studies across the coal chain from exploration and processing to utilization, and including environmental aspects. The output from this system provides a reflectance fingerprint on the maceral groups, and compositional information, particle density and ash value on each individual grain. This system also has the capability to identify the reflectance boundary between fusible and infusible inertinite in individual coal particles for Australian coking coals. When analyses are conducted on size fractions of coke oven feed coal (nominal top size of 4mm) the CGA results provide detailed information of the overall maceral and grain type composition of the entire sample and the size distribution of the macerals (including infusible and fusible organic inerts and minerals separately) and grain types and the association between macerals and minerals in the individual grains for the coke oven feed samples.

The objectives of this project were to enhance the CGA system and to use the system to:

• Determine the relationship between rank and the fusible reflectance range for an additional six coals from different Australian coal basins;
• Characterise coal blends;
• Investigate the transformation of major minerals during Coking;
• Validate the CGA analysis of standard petrographic samples to determine the fusible and infusible constituents.

During project C21059, the CGA system was used to analyse matched coal and coke halves to determine the fusible reflectance range for six Australian coking coals of different ranks. These results showed that the reflectance range for the fusible inertinite was greatest for the lowest rank coals and decreased with increasing rank. The first goal of this project was to analyse an additional six Australian coals using the same methodology, increasing the total number of samples to twelve, which allowed us to confirm the relationship between the fusible inertinite reflectance range and coal rank identified during C21059.

The second project goal was to modify the CGA system to analyse coal blends to provide:

• Details on the overall size distribution of the coals in the blend;
• Maceral and grain type abundances for the individual coals in simple blends; and
• Breakdown of inertinite into fusible and infusible inertinite for each coal.

The third objective of the project was to investigate mineral transformation during coking and mineral interactions with the organic matrix by analysing the matching individual mineral grains in the coal and coke sample halves. This approach identified that the size and compositional transformation of minerals during the coking process is primarily based on the chemical composition of the original minerals and their associations with the organic material within the parent coal particles and in the resulting coke material. More work is, however, required to obtain a better understanding of the evolution of mineral phases and the mineral/maceral interactions that may have occurred during coking.