Open Cut » Coal Extraction
This project dealt with the development of new techniques to provide in-situ and off-belt bulk analysis of coal for: slagging index; density; ash content; direct estimates of silica (Si), alumina (Al) and iron content (Fe). The technique employed was prompt gamma neutron activation.
The general objectives of the project were:
- To expand on the capabilities of the spectrometric neutron-gamma technique for predicting, in-situ, the slagging of coal, density, calorific value and chemical constituents of the coal ash such as Si, Al and Fe.
- Investigate this technique for off-belt bulk analysis using a 4p geometry similar to that employed for borehole logging.
The work undertaken for this project was carried out at the CSIRO Exploration and Mining, Queensland Centre for Advanced Technologies Laboratory. The project consisted of two stages:
The first stage investigated the application of the neutron-gamma technique to borehole logging. The aim of this research was to extend the capabilities of this technique for the determination in boreholes of the slagging index of the coals, their chemical contents of Si and Al and their density. This technique had been developed previously for the identification of the coal seams and the determination of their ash and Fe content.
The second stage consisted of investigating the neutron-gamma technique for off belt bulk analysis of coal in a 4p geometry.
Borehole Logging
Callide Coalfields:
Logging data from fifteen cored exploration holes was available for the present work. Multiple regression analysis was used to test the accuracy of the neutron-gamma tool for the determination of ash and iron in coal, techniques already developed and used in the Australian coal industry.
The capability of the neutron-gamma tool for the determination of Si, Al, density and slagging index of coal was then thoroughly investigated.
Theodore Coals:
Eight cored holes were logged with the neutron-gamma tool. The core was analysed in the laboratory and the assays were made available to the CSIRO. CSIRO undertook a thorough analysis of the logging and laboratory data in order to enhance the capabilities of the neutron gamma technique for coal logging. Data analysis and interpretation was similar to the data interpretation carried out at Callide Coalfields.
Off-Belt Analysis
The neutron-gamma technique was tested for bulk sample analysis of coal. Fifteen bulk coal samples were prepared from samples taken from Callide Coalfields. The samples were thoroughly mixed and analysed for ash content and chemical composition of the ash. The samples were then placed in large tapered plastic drums which had a 4p geometry. This 4p geometry resembles borehole geometry. Neutron-gamma measurements were taken with the borehole logging tool that was used for logging the cored boreholes.
The 4p geometry chosen in this work is different from the geometries normally used in static bulk analysis or on-stream analysis. The 4p geometry is the most efficient geometry allowing the use of lower activity sources without decrease in counting statistics and accuracy. This geometry can also be adapted for off-belt on stream analysis.
Project Outcomes
The present work has extended the capabilities of the neutron-gamma technique for borehole logging of coal.
An important outcome is the development of the tool for the determination of density in boreholes. It is widely accepted that the backscattered gamma-gamma technique is 'the technique' for density measurements in boreholes and the gamma-gamma tool is always selected for density measurements. This work demonstrates that the neutron-gamma tool can also be used for density measurements. This development makes neutron-gamma a powerful technique for coal logging.
The work carried out under this grant demonstrates that the neutron-gamma technique is capable of predicting the deformation temperatures for coals for which a correlation exists between deformation temperature and the percentage of Al, Si and Fe present in coal. However this technique does not work in coal deposits where such correlations do not exist. In the present work, neutron-gamma successfully predicted the deformation temperature for Theodore Coals but failed to predict this temperature for the coal from the Callide Coalfields.
The neutron-gamma technique developed by the CSIRO for coal borehole logging has been commercialised and is available to the coal mining industry. By comparison to the commercial gamma-gamma technique that measures the density and ash content of coal, the neutron-gamma measures simultaneously the density, ash, Al, Si and Fe of coal. The deformation temperature can also be determined in boreholes in some coal deposits.
The present work also demonstrated that the neutron-gamma technique can be used for off-belt bulk analysis of coal in a borehole like 4>p geometry. This is a more efficient geometry than others employed for bulk analysis. The ash, Al, Si and Fe content of coal were determined with good accuracy.